WO2020052957A1

WO2020052957A1 - Arrangement for amplifying an input signal

Info

Publication number: WO2020052957A1
Application number: PCT/EP2019/072769
Authority: WO
Inventors: Frits Tobi DE JONGH; Paul Theodorus Jacobus BOONEN
Original assignee: Signify Holding B.V.
Priority date: 2018-09-10
Filing date: 2019-08-27
Publication date: 2020-03-19

Abstract

A modulating amplifying arrangement for amplifying an input signal that accounts for noise introduced by the modulating operation. An input signal is modulated, to obtain a modulated signal, and subsequently amplified to obtain an amplified modulated signal. This amplified modulated signal is then sampled by an analogue-to-digital converter to thereby obtain amplified samples of the input signal. The modulated signal is biased by a biasing arrangement to account for a voltage offset introduced into the amplified samples by the modulating of the input signal.

Description

Arrangement for amplifying an input signal

FIELD OF THE INVENTION

The present invention relates to the field of amplifiers, and in particular to the field of amplifiers for an alternating current (AC) signal. BACKGROUND OF THE INVENTION

There has been an increasing interest in amplifiers for low-magnitude and low- frequency alternating current (AC) signals. One known method is to use a chopper amplifier to amplify such signals. Chopper amplifiers help avoid pink noise, mains supply interference and (parasitic) piezoelectric noise introduced by vibrations.

A chopper amplifier operates by chopping an input signal at a frequency greater than a frequency of interest (i.e. an AC component) in the input signal. The chopped signal is then amplified to produce an amplified chopped signal. The amplified chopped signal can then be smoothed, e.g. using a capacitor arrangement, to generate an amplified version of the input signal.

Signals of higher frequencies suffer less from the aforementioned noise sources than signals of lower frequencies during an amplification process. Thus, by converting the input signal into a signal of a higher frequency before amplification, these noises can be mitigated during the amplification process.

There is an ongoing desire to further improve the noise reducing properties of amplifiers of AC signals.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided an amplifying arrangement for amplifying an input signal of a first frequency. The amplifying arrangement comprises a modulating arrangement adapted to receive the input signal and generate a modulated signal that alternates, at a second frequency, between a current voltage level of the input signal and a reference voltage level, the second frequency being greater than the first frequency. The amplifying arrangement also comprises an amplifying circuit adapted to amplify the modulated signal to thereby provide an amplified modulated signal. The amplifying arrangement also comprises an analogue-to-digital converter adapted to perform a first sampling operation comprising sampling the amplified modulated signal at the second frequency and in phase with portions of the amplified modulated signal corresponding to amplifications of the input signal, to thereby obtain first amplified samples of the input signal. The amplifying arrangement also comprises a biasing arrangement adapted to bias a magnitude of the modulated signal to thereby account for a voltage offset introduced by the modulating arrangement in the first amplified samples.

There is therefore proposed a concept of an amplifying arrangement for an input signal that chops or modulates the input signal prior to amplification, where the modulated signal is biased to account for a voltage offset in an output of the amplification.

It has been recognized that modulating an input signal, to generate a modulated signal that switches between an input signal and a reference voltage, introduces noise or error in the modulated signal. In particular, switching a connection between an input signal and a reference voltage level introduces noise at a same frequency as the switching. Thus, modulating causes noise to be introduced into the modulated signal at the frequency of modulating (i.e. at the second frequency). This noise is then propagated through the amplifying circuit and would usually be present in the amplified samples of the input signal.

However, as the noise introduced by modulating or switching (i.e. modulating noise) is at the frequency of modulating, it has been recognized that the end result of this noise is the introduction of a bias or a voltage offset in those portions of the (amplified) modulated signal that correspond to the input signal, and thereby in the first amplified samples. In particular, there is an undesirable voltage offset across samples of the (amplified) modulated signal taken at the second frequency. Thus, in samples taken at the modulation frequency, there is a sample voltage offset in each sample. This bias or voltage offset leads to distortion and/or clipping problems when amplifying the modulated signal using the amplifying circuit.

The present invention proposes to bias the modulated signal to take account of the voltage offset introduced in the portions of the modulated signal that correspond to the input signal (i.e. carrying instantaneous input signal information). This results in the input signal portions of the modulated signal, being those portions which are sampled by the analogue-to-digital converter (ADC), being biased with an aim of mitigating the offset introduced by the modulating process. This reduces a distortion of the input signal portions during amplification (e.g. clipping or the like), as a voltage offset has been accounted for. In particular, the biasing arrangement may be adapted to bias the modulating signal to account for a voltage offset introduced at the portions or points of the modulating signal that correspond to the portions or points of the amplified modulating signal sampled by the analogue-to-digital converter. This means that the sampled portions of the amplified signal have (pre-amplification) been biased to account for noise introduced by modulating. In this way, the first amplified samples are samples of those parts of the (amplified) modulating signal that have been biased by the biasing arrangement.

It will be clear that a magnitude of the biasing may change over time (i.e. the biasing is dynamic) to account for changes in the voltage offset introduced by the modulating arrangement. Such changes in the effective voltage offset may be due, for example, to temperature effects, such as thermal degradation of components, or introduction of additional noise. Thus, it will be clear that the magnitude of the biasing may be continually assessed and revised, rather than being performed only on start-up of the amplifying arrangement.

The biasing arrangement may be adapted to bias a magnitude of the modulated signal based on magnitudes of the first amplified samples of the input signal obtained by the analogue-to-digital converter.

By taking into account the magnitudes of the first amplified samples, a biasing of the modulated signal can be made more accurately, as the effect of the modulating noise on the amplified samples can be taken into account.

Preferably, the biasing arrangement is adapted to determine an average magnitude of the first amplified samples of the input signal and bias the magnitude of the modulated signal for the amplifying circuit based on the average magnitude of the first amplified samples of the input signal.

It has been recognized that the amount of modulating noise introduced by the modulating arrangement may gradually change or drift over time. Moreover, it can be assumed that an average of input signal remains substantially constant over time. The average magnitude of the first amplified samples may be taken over a predetermined period of time (e.g. 1 second, 30 seconds, 1 minute, 5 minutes or so on). The average magnitude may be a moving average, for improved tracking of the voltage offset.

Thus, a change in the average of the first amplified samples can be indicative that a change in magnitude of modulating noise has occurred, and that there is therefore an undesirable voltage offset in the amplified samples, and in the portions of the modulated signal corresponding to the input signal. Thus, by biasing the magnitude of the modulated signal based on the average magnitude of the first amplified samples, an undesirable voltage offset in the samples (and portions of the modulated signal containing input signal information) can be mitigated.

Even more preferably, the biasing arrangement is further adapted to determine a quiescent voltage of the amplifying circuit and bias the magnitude of the modulated signal for the amplifying circuit based on a difference between the quiescent voltage of the amplifying circuit and the average magnitude of the first amplified samples of the input signal.

Conventionally, an input of an amplifying circuit is biased to a midpoint of a voltage supply and ground for the amplifying circuit, in order to maximize the potential voltage swing of the amplifying circuit. The biasing point, typically the midpoint, is often called the quiescent point, and corresponds to a quiescent voltage.

The biasing arrangement can therefore be adapted to bias the magnitude of the modulated signal based on the difference between the average of the first amplified samples and the quiescent voltage. This may be performed with the aim of minimizing or reducing a drift of the first amplified samples from the quiescent voltage of the amplifying circuit.

Thus, the biasing arrangement may be adapted to bias the magnitude of the modulated signal so that an average of future first amplified samples of the input signal is approximately the same magnitude as the quiescent voltage of the amplifying circuit.

Thus, the biasing arrangement may be designed so as to bring an average of the first amplified samples into line with the quiescent voltage of the amplifying

arrangement. This effectively maximizes the potential voltage swing of the first amplified samples and helps to reduce the change of clipping or other distortion issues in the portions of the amplified modulated signal that are sampled to create the first amplified samples.

In another embodiment, the biasing arrangement is adapted to generate a biasing signal that alternates, at the second/modulating frequency, between a second reference voltage level and a third reference voltage level, wherein the biasing signal is used to bias a magnitude of the modulated signal. Thus, a biasing signal that models noise introduced by a modulating arrangement can be subtracted from the modulated signal to thereby more accurately account for the noise introduced by the modulating arrangement.

Preferably, the reference voltage level is an average of the input signal.

By setting or controlling the reference voltage level to be an average of the input signal, a voltage swing of the overall modulated signal can be minimized. This enables the amplifying circuit to have a greater gain, without reduced risk of clipping or other distortions to the amplified modulated signal. This further reduces noise in the amplified modulated signal, and therefore in the first amplified samples of the input signal.

The modulating arrangement may comprise a first modulating input terminal adapted to receive the input signal, a second modulating input terminal adapted to receive the reference voltage level, a modulating output terminal, and switching logic adapted to alternately connect, at the second frequency the modulating output terminal to the first modulating input terminal and the second modulating input terminal, to thereby generate the modulated signal on the modulating output terminal.

Thus, the modulating arrangement may comprise a switch that alternately connects the reference voltage level and the input signal to an output terminal, thereby producing a modulated signal with a voltage level that alternates between the reference voltage level and a current voltage level of the input signal. Other suitable modulating arrangements will be known to the person skilled in the art.

The amplifying arrangement may further comprise a reference voltage level generator formed of: a capacitor connected between the second modulating input terminal and a ground voltage; and a resistor connected between the modulating output terminal and the second modulating input terminal, so that a voltage level at the second modulating input terminal is held at an average of the input signal.

Such a reference voltage level generator provides compact and simple circuit that supplies a reference voltage level having an average of the input signal, without the need to provide any additional biasing elements or large storage components. Thus, the advantages of having a reference voltage level at the average of the input signal can be realized without the need for a significant number of additional components.

The reference voltage level generator may be replaced by any other suitable reference voltage generator that generates a reference voltage level, e.g. based on magnitude characteristics of the input signal such as an average magnitude.

In some embodiments, the amplifying arrangement applies a low-pass filter or band-pass filter to the modulated signal or the amplified modulated signal, the low-pass or band-pass filter being adapted to pass the second frequency; and the analogue-to-digital converter is adapted to perform a second sampling operation comprising sampling the amplified modulated signal at the second frequency and synchronized with portions of the amplified modulated signal corresponding to amplifications of the reference voltage level, to thereby obtain second amplified samples of the input signal. It has been recognized that performing a low-pass or band-pass filter on the (amplified) modulated signal results in an amplified signal that contains input signal information twice within a single period of the amplified signal. In other words, by applying a band-pass filter to the (amplified) modulated signal, a portion of the (amplified) modulated signal that previously corresponded to the reference voltage level is converted into a portion that also contains instantaneous information on the input signal.

Thus, by performing a second sampling operation on the amplified modulated signal, second amplified samples of the input signal (each corresponding to a respective first amplified sample) can be obtained.

The second amplified samples may be used to improve a resolution and/or gain of the amplifying arrangement or to verify an accuracy of the first amplified samples. Other uses for the second amplified samples will be readily apparent to the skilled person.

The analogue-to-digital converter can be adapted to determine a difference between each first amplified samples of the input signal and an immediately preceding or following second amplified samples of the input signal to derive third amplified samples of the input signal. By determining a difference between the first and second amplified samples (“third amplified samples”), an amplified sample having a greater magnitude than either alone can be determined. This effectively increases the resolution and gain of the amplifying circuit, as well as reducing signal uncorrelated noise.

In at least one embodiment, the amplifying arrangement further comprises a digital-to-analogue converter adapted to: receive an output of the analogue-to-digital converter; and convert the output of the analogue-to-digital converter into an analogue output signal, the analogue output signal thereby representing an analogue amplification of the input signal.

There may be provided a sensing arrangement comprising: any previously described amplifying arrangement, a sensing module adapted to generate a sensing signal for amplification, the sensing signal carrying information of interest at the first frequency, wherein the amplifying arrangement receives the sensing signal output by the as the input signal.

The sensing module may comprise a transmission circuit adapted to transmit an electromagnetic wave; a sensing circuit adapted to: receive a reflection of the transmitted electromagnetic wave; determine a difference in frequency between the transmitted electromagnetic wave and the reflection of the transmitted electromagnetic wave; and output a sensing signal having a frequency equal to the difference in frequency; and any amplifying arrangement previously described, wherein the sensing signal output by the sensing circuit is received as the input signal. Preferably, the electromagnetic wave is a radio wave.

Embodiments of the invention are particularly effective when employed with low-frequency, low-magnitude signals, such as those produced by a sensing arrangement operating on the Doppler principle.

According to examples in accordance with an aspect of the invention, there is provided a method for amplifying an input signal of a first frequency. The method comprises receiving the input signal and generating a modulated signal that alternates between a current voltage level of the input signal and a reference voltage level at a second frequency, the second frequency being greater than the first frequency. The method also comprises amplifying, using an amplifying circuit, the modulated signal to thereby provide an amplified modulated signal. The method also comprises performing a first sampling operation comprising sampling the amplified modulated signal at the second frequency and in phase with portions of the amplified modulated signal corresponding to amplifications of the input signal, to thereby obtain first amplified samples of the input signal. The method further comprises biasing a magnitude of the modulated signal to thereby account for a voltage offset introduced at the second frequency in the portions of the modulated signal corresponding to the input signal by the generating of the modulated signal.

Optionally, the step of biasing comprising biasing the magnitude of the modulated signal for amplification based on the first amplified samples of the input signal obtained by the analogue-to-digital converter.

In some embodiments, the step of biasing comprises: determining an average magnitude of the first amplified samples of the input signal; determining a quiescent voltage of the amplifying circuit; and biasing the magnitude of the modulated signal for amplification based on a difference between the quiescent voltage of the amplifying circuit and the average magnitude of the first amplified samples of the input signal.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure 1 illustrates an amplifying arrangement according to an embodiment of the invention;

Figures 2 to 5 illustrate explanatory signal waveforms for understanding an operation of the amplifying arrangement according to an embodiment;

Figure 6 is a circuit diagram of parts of an amplifying arrangement according to an embodiment of the invention;

Figure 7 illustrates waveforms for understanding an operation of an amplifying arrangement according to another embodiment;

Figure 8 illustrates an amplifying arrangement according to another embodiment of the invention;

Figure 9 is a flow chart illustrating a method according to an embodiment of the invention; and

Figure 10 illustrates a sensing arrangement according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the Figures.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

According to a concept of the invention, there is proposed a modulating amplifying arrangement for amplifying an input signal that accounts for noise introduced by the modulating operation. An input signal is modulated at a modulating frequency, to obtain a modulated signal, and subsequently amplified to obtain an amplified modulated signal. This amplified modulated signal is then sampled (at the modulating frequency) by an analogue-to- digital converter to thereby obtain amplified samples of the input signal. The modulated signal is biased by a biasing arrangement to account for a voltage offset introduced into the amplified samples by the modulating of the input signal. Embodiments are at least partly based on the realization that modulating of an input signal, to form a modulated signal, introduces noise in the modulated signal at a modulating frequency. In particular, it has been recognized that, if an amplified version of this modulated signal is sampled by an ADC at the modulating frequency (i.e. to produce an amplified input signal), the noise at the modulating frequency is seen as a voltage offset in each ADC sample. Thus, it is possible to bias the modulated signal to take account of the noise introduced during modulating of the input signal, so that the voltages sampled by the ADC are more accurate and less subject to distortion by the amplifier.

Illustrative embodiments may, for example, be employed in RADAR sensors in which a difference between an emitted electromagnetic wave and a received

electromagnetic wave is provided as an input signal for the amplifying arrangement. Such RADAR sensor typically provide signals of a low amplitude and low frequency (<500Hz) and are therefore highly subject to noise (e.g. pink noise or mains supply noise) during an amplification process. The proposed amplifying circuit enables accurate amplification of low amplitude and low frequency signals with an improved signal-to-noise ratio.

According to another embodiment, there is proposed another modulating amplifying arrangement for amplifying an input signal. An input signal is modulated at a modulating frequency between the input signal and a reference voltage, to obtain a modulated signal, and subsequently amplified to obtain an amplified modulated signal. This amplified modulated signal is then sampled at portions of the amplified signal that correspond to the input signal and portions of the amplified signal that correspond to the reference voltage level, to thereby obtain alternating first and second samples of the amplified modulated signal. A difference between immediately consecutive first and second samples can be determined, to thereby determine third samples representing amplified samples of the input signal.

Such embodiments are at least partly based on the realization that input signal information is available twice during a single period of an amplified modulated signal. In particular, when an amplifying circuit performs a low-pass or band-pass filter on a modulated signal, this results in the amplified modulated signal comprise input signal information at both turning points within a single period of an amplified modulated signal. This realization can be exploited to maximize a gain and/or resolution of the amplifying arrangement, and account for noise introduced by the modulating arrangement.

Such embodiments may, for example, also be employed in RADAR sensors to maximize a gain and resolution of amplifying arrangements for such RADAR sensors. Examples of both modulating amplifying arrangements will be hereafter described in the context of an amplifying arrangement employing both concepts. However, it will be appreciated that the two above-described embodiments may be realized separately and independently from one another.

The hereafter described amplifying arrangement(s) are particularly suitable for amplifying input signals having a very low amplitude variation or range (e.g. ±0.1 OmV) and a low frequency into an amplified signal in which these variations have been subject to a very large gain (e.g. > 15,000). Thus, the amplifying arrangement is particularly suitable for use in amplifying the output of a RADAR sensor, in which signals having a low frequency and low varying amplitude are typically generated.

Where reference is made to the frequency of a signal, this should be understood to refer to the dominant frequency of the signal - i.e. that frequency providing the largest contribution to a variation of the signal.

Figure 1 illustrates a block diagram of an amplifying arrangement 1 according to an embodiment of the invention. The operation of the amplifying arrangement 1 will be hereafter described with reference to Figure 1 and accompanying Figures 2 to 5 that illustrate signals present during the operation of the amplifying arrangement.

The amplifying arrangement 1 is formed of a modulating arrangement 2, an amplifying circuit 3, an analogue-to-digital converter 4 and a biasing arrangement 5.

The amplifying arrangement 1 acts as an analogue-to-digital amplifier that effectively obtains amplified samples (i.e. a digital signal) of an analog or time-continuous input signal Si_n. Of course, these amplified samples may be subsequently resolved into an analog signal, e.g. using a known digital-to-analogue converter, to obtain an analog amplification of the input signal Si_n.

The modulating arrangement 2 receives the input signal Si_n and generates a modulated signal s_mod. The modulating arrangement 2 is adapted so that the modulated signal S_mod alternates between the input signal Si_n and a reference voltage level V_ref. Thus, the modulated signal alternates between a voltage providing information on a

current/instantaneous value of an input signal and a reference voltage level (i.e. not providing information on a current/instantaneous value).

As illustrated, the modulating arrangement 2 may comprise a first input terminal 2a, adapted to receive the input signal Si_n, a second input terminal 2b adapted to receive the reference voltage level Vref and an output terminal 2c adapted to provide the modulated signal s_mod. Switching logic 2d is adapted to alternately connect the output terminal to the first input terminal 2a and then to the second input terminal 2b. The switching logic 2d may, for example, comprise a single pole double throw or changeover switch 2d controlled by a switching signal s_s that controls the connection of the output terminal 2c. The switching signal s_s may be provided by a microcontroller, processor, oscillating circuit or other control unit (not shown).

The frequency at which the magnitude of the modulated signal alternates between a current magnitude of the input signal Si_n and the reference voltage level V_ref (the “modulating frequency”,“modulation frequency” or“second frequency”) is larger than the frequency of the input signal Si_n (the“first frequency” or“input frequency”). In this way, the input signal Si_n is modulated or converted to form a modulated signal s_mod of a higher frequency, which contains information from the input signal Si_n.

The duty cycle of the modulated signal may be in the region of 10-50%. In a simple embodiment, the modulated signal may have a duty cycle of around 50%, so that it switches evenly and regularly between a voltage level of the input signal and the reference voltage level. In other embodiments, e.g. to reduce a power consumption of the amplifying arrangement, the duty cycle may be in the region of 10%, so that the modulated signal is held at the voltage level of the input signal Si_n for 10% of the time and at the reference voltage level V_ref for 90% of the time. The duty cycle of the modulated signal s_mod may be controlled to be any number between 10-50%, depending upon the embodiment. Of course, the duty cycle may, in some embodiments, be greater than 50%.

Figure 2 is a graph illustrating the relationship between the input signal Si_n and the modulated signal s_mod. In particular, Figure 2 illustrates a voltage waveform for an example input signal Si_n and a corresponding modulated signal s_mod, plotted along a same time axis.

The input signal Si_n is of a first frequency and the modulated signal s_mod is of a second frequency (i.e. the“modulating frequency”). Here, the second frequency is between two and twenty times greater than the first frequency, for example, around ten times greater than the first frequency or about four to eight times the first frequency. The second frequency should, to ensure proper signal reproduction by the analogue-to-digital converter, fulfill at least the Nyquist criteria with respect to the first frequency, as would be known by the skilled person. The second frequency may depend on different implementation requirements, such as required signal-to -noise ratio, the analog low pass filter roll-off and filter details in firmware, as would be well known to the skilled person. By way of example, the first frequency may be in the region of l-500Hz, e.g. around 200Hz, and the second frequency may be in the region of 1,500 to 2,500 Hz, and preferably around 2,000Hz. The size of the second frequency may depend upon the dominant frequency of the input signal Si_n. Preferably, the second frequency is at least 2,000Hz. This allows for improved ease and reduced cost for performing a low-pass filter on the modulated signal (if desired).

It will be clear that the magnitude or voltage level of the modulated signal s_mod alternates between a voltage level of the input signal Si_n and the reference voltage level V_ref.

In this way, the input signal Si_n is effectively sampled onto the modulated signal v_mod at the modulating frequency, where the modulated signal is held at the reference voltage level in between samples. In other words, the modulating arrangement modulates an input signal of interest onto a carrier signal of a higher frequency to produce the modulated signal s_mod.

Referring back to Figure 1 , the amplifying circuit 3 is adapted to amplify the modulated signal s_mod to generate an amplified modulated signal s_a.

The amplifying circuit may, as illustrated, be single ended or, preferably, have a differential input. A differential input allows for ease of biasing the modulated signal s_mod (e.g. as the modulated signal can be provided to one terminal and a biasing signal can be provided to the other terminal). For example, a negative terminal may be adapted to receive the modulated signal s_mod from the modulating arrangement and a positive terminal may be adapted to receive a biasing signal S_bias from the biasing arrangement, so that a differential signal amplified by the amplifying circuit is formed of a biased version of the modulated signal.

The amplifying circuit 3 may comprise one or more operational amplifiers, and other amplifying logic (e.g. feedback resistor/capacitors and the like) for amplifying the modulated signal. Other suitable amplifying circuits for amplifying a modulated signal would be readily apparent to the skilled person.

The amplifying circuit 3 may be provided with a voltage supply or power supply VDD and a ground voltage GND, as would be known to the skilled person.

In some (optional) embodiments, the amplifying circuit 3 applies a band-pass or low-pass filter to the modulated signal s_mod before or during amplification. The filter would be adapted to pass a signal of the modulating/second frequency. For example, a band- pass filter may be centered at the modulating frequency. This improves a signal-to -noise ratio. The gain of the amplifying circuit may depend upon the characteristics or nature of the input signal Si_n. However, embodiments of the invention may comprise an amplifying circuit having a gain between 50dB and 90db (e.g. a gain factor of approximately 500 to 30,000). Preferably, the gain factor is no less than 15,000 (around 83.5dB), and even more preferably no less than 20,000 (around 86dB).

Figure 3 is a graph illustrating the relationship between the modulated signal S_mod and the amplified modulated signal s_a. In particular, Figure 3 illustrates a waveform of an exemplary modulated signal s_mod and a corresponding amplified modulated signal s_a, plotted along a same time axis.

The amplifying arrangement here performs an inverting amplification to the filtered modulated signal to produce the amplified modulated signal. It will be appreciated that Figure 3 is not to scale, and that the amplification performed by the amplifying arrangement may differ (e.g. have a gain of no less than 15,000).

In the illustrated examples, a band-pass filter (or low-pass filter) has been applied to the modulated signal s_mod before/during amplification, so that the filtered

(amplified) modulated signal has only a narrow band of frequencies, including the modulating frequency.

This has the effect of creating an amplified modulated signal in which input signal information is contained both in portions corresponding to portions of the modulated signal corresponding to the input signal and to portions of the modulated signal

corresponding to the reference voltage level. As later explained, this effect can be exploited to improve a resolution or gain of the amplifying arrangement. In other embodiments, however, no-band pass filter is applied to the modulated signal s_mod.

Again referring back to Figure 1, the analogue-to-digital converter 4 is adapted to sample the amplified modulated signal s_a at the modulating frequency, and in phase with the portions of the amplified modulated signal that correspond to amplifications of the input signal.

In other words, when performing a first sampling process or operation, a sampling frequency of the analogue-to-digital converter is equal to the modulating frequency or“second frequency” of the modulating arrangement 2, where the samples are taken across portions of the amplified modulated signal that correspond to portions of the modulated signal that contain (instantaneous or current) information of the input signal. Thus, the samples taken during the first sampling process or operation of the analogue-to-digital converter are amplified samples of the input signal Si_n. In this way, the amplifying arrangement can amplify the input signal.

Preferably, the analogue-to-digital converter is adapted to sample the amplified modulated signal s_a at turning points of the amplified modulated signal (i.e. at a maximum or minimum points of each cycle of the amplified signal). This increases the resolution of the amplifying arrangement, ensuring that the points of the amplified modulated signal that represent the maximum amplifications of the relevant portions of the modulated signal corresponding to the input signal are sampled.

When sampling the amplified modulated signal s_a, it may be necessary to take into account a phase delay resulting from (the transfer function of) the amplifying circuit. Put another way, the amplifying circuit may introduce a phase shift between the amplified modulated signal and the modulated signal, such that amplified portions of the input signal (in the amplified modulated signal) are out of phase with the corresponding portions of the input signal (in the modulated signal).

To take account of this phase shift by the amplifying circuit, the sampling by the analogue-to-digital converter may have a same frequency, but be phase-shifted, with respect to the modulating of the input signal performed by the modulating arrangement. Preferably, this phase shift is determined experimentally. In other examples, the phase shift is determined by calculating a transfer function of the amplifying circuit (e.g. from known component values) and determining a phase shift of the amplifying circuit. Without taking account of the phase shift, the sampling by the analogue-to-digital converter may be inefficient (i.e. not sampling at the greatest peak of the amplified modulated signal) and/or inaccurate. However, it is noted that for a modulated signal having a duty cycle of 50%, a phase shift of 90° is a reasonable estimation. In other words, the sampling by the analogue- to-digital converter may be 90° (or another values calculated as previously described) out of phase with the modulating by the modulating arrangement, in order to take account of a phase shift by the amplifying arrangement. The phase shift may therefore depend upon the duty cycle of the modulated signal (i.e. the proportion of the modulated signal that corresponds to the input signal Si_n rather than the reference voltage level V_ref).

Preferably, each sample taken by the analogue-to-digital converter during the first sampling process is timed to be at a center of a portion of the amplified modulated signal corresponding to a portion of the modulated signal corresponding to the input signal. For example, if a portion of the modulated signal corresponding to an input signal has length 0.5ms the sample taken by the analog-to-digital converter may correspond to a value of the amplified modulated signal 0.25ms into the corresponding portion of the amplified modulated signal.

Figure 4 illustrates a relationship between a sample result signal s_adc produced by the analogue-to-digital converter 4 and the amplified modulated signal s_a.

In particular, Figure 4 illustrates a waveform of an exemplary amplified modulated signal s_a, a sampling signal s_samp and a sample result signal s_adc The sampling signal s_amp indicates timestamps or instances at which first samples of the amplified signal s_a are taken.

The sample result signal s_adc indicates a value of a most recent sample. Thus, the sample result signal s_adc is a signal where the voltage level is held at the voltage level of a most recent (first) sample of the amplified modulated signal until a new (first) sample is taken. Thus, the sample result signal s_adc represents the values of first samples taken by the analogue-to-digital converter 4.

The first samples taken by the analogue-to-digital converter (as shown by the sampling signal s_samp) are taken at portions of the amplified modulated signal that correspond to an amplification of the input signal portions of the modulated signal. In this way, the first samples are considered amplified samples of the input signal Si_n, or“first amplified samples” of the input signal Si_n.

The sample result signal s_adc is an analog representation of the first samples of the input signal. Thus, the sample result signal s_adc can be considered to be an analog amplification of the input signal.

It will therefore be appreciated that, in some embodiments, there is further provided a digital-to-analogue converter adapted to: receive an output of the analogue-to- digital converter; and convert the output of the analogue-to-digital converter into an analogue output signal, the analogue output signal thereby representing an analogue amplification of the input signal.

The present invention recognizes that noise at the modulating frequency (i.e. “modulating noise”) is introduced into the modulated signal by the modulating arrangement 2. This modulating noise may be introduced, for example, by a switch leakage current (by the switching logic 2d) or a switch charge injection. As such, the modulating noise has a same frequency as the dominant frequency of the modulated signal. This results in errors in the samples taken by the analogue-to-digital converter, as the modulating noise is propagated through the amplifying arrangement. However, it has also been identified that the modulating noise is substantially regular, i.e. one period of the modulating noise is substantially identical to an immediately following period of the modulating noise. The results in the modulating noise causing a voltage offset across the amplified first samples taken by the analogue-to-digital converter.

Accordingly, it has been recognized that the modulated signal can be biased with a view to correcting this voltage offset in the amplified samples. In particular, by appropriately biasing the modulated signal to account for modulating noise, any distortion or clipping in subsequently samples of the amplified modulated signal can be avoided.

As the analogue-to-digital converter only samples the amplified modulated signal at a modulating frequency, it has been recognized that noise or distortion in other portions of the modulated signal (that do not correspond to portions that are sampled when amplified) could be ignored. Put another way, distortion in non-sampled portions of the amplified signal does not affect the accuracy of the amplification process. It is therefore only important to bias the modulated signal to account for errors introduced by the modulating noise in those portions of the modulated signal that are, when amplified, sampled by the analogue-to-digital converter.

Thus, the present invention proposes to bias the modulated signal to account for a voltage offset of the samples taken by the analogue-to-digital converter caused by modulating noise introduced by the modulating arrangement.

For the sake of improved understanding, Figure 5 illustrates a relationship between noise s_n at the modulating frequency (introduced by the modulating arrangement) and a sampling signal s_Sam_P. The sampling signal s_Sam_P indicates the times at which the analogue-to-digital converter samples the amplified modulated signal - i.e. a time at which the held signal s_adc of Figure 4 changes. Thus, the sampling signal s_sam_P indicates a timing or timestamp at which a sample of the modulated signal (not shown) is taken. It should be noted that the modulating noise s_n is in phase (and effectively superimposes) on the modulated signal (not shown in Figure 5).

From Figure 5, it will be seen that the noise s_n that is introduced by the modulating arrangement has a same frequency as the sampling process. As the noise s_n is periodic (i.e. every period of the noise s_n is substantially identical to the next), this effectively induces a same voltage offset at each timestamp when a sample is taken by the analogue-to- digital converter. This is because the voltage level of the modulating noise (in the amplified modulated signal) is substantially the same each time a sample of the amplified modulated noise is taken by the analogue-to-digital converter. Thus, it has been recognized that biasing the modulated signal s_mod can account for this effective voltage offset in the amplified samples.

The biasing arrangement 5 illustrated in Figure 1 provides a system for suitably biasing the modulating signal s_mod to account for the voltage offset in the amplified samples taken by the analogue-to-digital converter.

The biasing arrangement 5 comprises a bias determination unit 5 a and a current injector 5b that is adapted to modify a voltage level of the modulated signal s_mod based on a signal from the bias determination unit 5a. Thus, the current injector generates a biasing signal that biases, modifies or offsets a magnitude of the modulated signal s_mod. The bias determination unit 5 a is adapted to determine the magnitude and other characteristics of the bias or voltage offset to be applied to the modulated signal s_mod.

Here, the biasing determination unit 5 a is adapted to determine an average of the amplified samples taken by the analogue-to-digital converter 4. Determination of an average of amplified samples can be readily performed in the digital domain (to which the samples taken by the analogue-to-digital converter belong).

Preferably, the average is taken over at least one period of the input signal. In other examples, the average is taken over at least 1 second, for example, no less than 5 seconds, such as no less than 1 minute or no less than 10 minutes. The greater the time the average is taken over, the less reactive to instantaneous (and perhaps temporary) changes to the offset.

It has been recognized that if the average of the amplified samples are offset from a midscale/quiescent voltage point of the amplifier circuit, then the average of the portions of the modulated signal corresponding to the input signal are also offset from this point. This would result in the portions of the modulated signal corresponding to the input signal being more susceptible to distortion and/or clipping when amplified.

Thus, the biasing determination unit 5a may compare the average of the amplified samples to a quiescent voltage of the amplifying circuit. Typically, the quiescent voltage of the amplifying circuit is a half way point, or midscale voltage point, between a voltage supply VDD for the amplifying circuit and a ground voltage GND for the amplifier circuit (to maximize the potential voltage swing of the amplifier circuit).

The bias determination unit 5a then controls the current injector 5b to bias the modulated signal s_mod to bring the average of the amplified samples into line with the quiescent voltage of the amplifying circuit. Biasing the modulated signal s_mod may take place at an input to a differential amplifier of the amplifying arrangement. For example, the modulated signal s_mod may be provided as an input to a first node (e.g. negative input terminal) of the differential amplifier, and a current injected by the bias determination unit may be provided as an input to a second node (e.g. positive input terminal) of the differential amplifier. This enables the effective modulated signal (i.e. that signal which is amplified) to be biased by the current provided by the current injector 5b.

In other words, the biasing arrangement 5 may aim to bias the modulated signal so that an average magnitude of the amplified samples taken by the analogue-to-digital converter is equal to a quiescent voltage (e.g. midscale voltage point) of the amplifying circuit.

This results in the portions of the modulated signal (which, when amplified, are sampled and also correspond to the input signal) are averaged around the quiescent voltage (e.g. midscale voltage point) of the amplifying circuit. This thereby reduces a distortion of the amplifying circuit for those portions of the modulated signal (e.g. avoids clipping) and allows the resolution of the amplifying circuit (i.e. gain) to be increased.

This results in subsequent samples of the amplified modulated signal being more accurate, and less subject to noise and/or variation. Thus, the accuracy of the amplifying circuit can be improved and a signal-to-noise ratio (SNR) can be improved.

One example of a current injector 5b is a resistor, controllable by changing a voltage supplied to the resistor (e.g. by the bias determination unit).

In this way, the biasing arrangement 5 biases or offsets the modulated signal S_mod based on the magnitudes of the first amplified samples of the input data. In particular, the biasing arrangement 5 biases the modulated signal based on a difference between an average of magnitudes of the first amplified samples and a quiescent voltage of the amplifier circuit, with an aim to minimize this difference.

In a simple embodiment, biasing arrangement 5 may introduce a DC offset into the modulated signal to account for the effective voltage offset occurring in the samples of the amplified signal.

In another example, the biasing arrangement 5 is adapted to inject an alternating signal at the modulating frequency (i.e. the second frequency) into the modulated signal to counteract noise at the modulating frequency introduced by the modulating arrangement. This injected alternating signal is preferably a signal that is out of phase with the modulating noise. This helps further reduce the noise across all portions of the modulated signal s_mod, which can prevent overload of the amplifying circuit.

The bias determination unit 5 a and the analogue-to-digital converter 4 may be combined into a same micro-processing unit.

As illustrated in Figure 1 , the amplifying arrangement may also comprise a reference voltage generator 6. This may be formed as part of the modulating arrangement 2. The reference voltage generator 6 provides the reference voltage level V_ref for use in the modulated signal s_mod.

In particular, the reference voltage level Vref has a magnitude based on one or more magnitude characteristics of the input signal. In preferable embodiments, the reference voltage level is generated so that the voltage swing of the modulated signal is no greater than the voltage swing of the input signal. This improves a resolution of the amplifying arrangement and avoids saturation (or gain limitation) of the amplifying circuit.

Here, the reference voltage generator 6 is adapted to provide an average of the input signal Si_n as the reference voltage level.

The reference voltage generator 6 here comprises a capacitor 6a, for storing charge, and a resistor 6b for controlling a charge across the capacitor 6a. The capacitor 6a is connected to the second input terminal 2b of the modulating arrangement 2, so that the voltage across the capacitor is the reference voltage level for the modulated signal s_mod. The other end of the capacitor is connected to a ground voltage GND.

The resistor is connected between the output terminal 2c and the second input terminal 2b of the modulating arrangement 2. Thus, when the modulating arrangement 2 connects the first input terminal 2a to the output terminal 2c, the resistor 6b begins to pull the voltage across the capacitor 6a towards the level of the input signal. When the modulating arrangement switches the connection, and connects the second input terminal 2b to the output terminal 2c, the voltage across the capacitor 6 is provide as the portion of the modulated signal s_mod, and the resistor 6b maintains the voltage across the capacitor. The process is iteratively repeated as the modulating arrangement switches back and forth between the two input terminals 6a, 6b.

Over time, this process results in the voltage across the capacitor, i.e. the reference voltage level Vref, approximately equaling the average voltage of the input signal

Sin·

Thus, between samples of the input signal Si_n, the modulated signal is held at an average voltage of the input signal Si_n. This helps avoid an amplifier saturation and improve a resolution of the amplifying arrangement, as the relative variance of the modulated signal is substantially less than in a conventional modulating mechanism where the modulated signal is held at a ground level between samples of the input signal. In other words, the range of values in the modulated signal s_mod provided to the input of the amplifying circuit is reduced, meaning that the amplifier may apply a greater gain to the modulated signal s_mod without risking clipping or distortion in the amplified signal. The reference voltage generator 6 thereby acts as pedestal cancelation circuity.

This arrangement is fundamentally different from a known sample-and-hold implementation for sampling the input terminal, as there is no intention to identify the instantaneous value of the input signal - rather the reference voltage generator aims to store a value outside the bandwidth of interest.

Figure 6 illustrates a circuit diagram of an amplifying arrangement 60 according to an embodiment of the invention.

The amplifying arrangement again comprises a modulating arrangement 2, an amplifying arrangement 3, a biasing arrangement 5 and a reference voltage generator 6. The analogue-to-digital converter has been omitted for the sake of clarity.

The amplifying arrangement 3 comprises a cascading pair of operational amplifier Ul and U2. Each operation amplifier Ul, U2 comprises feedback logic R5-R7, C5- C7, and other components R4, C4, R8, designed to provide a bandwidth limited amplifying circuit. In other words, the feedback logic of the amplifying arrangement is designed so as to apply a band-pass filter on the modulated signal during/before amplification.

In particular, the amplifying circuit 3 illustrates a cascaded low-pass amplifier (associated with the operational amplifier Ul) and high-pass amplifier (associated with the operational amplifier U2), with the two cut-off (roll-off) frequencies being centered at the second frequency (i.e. at the“modulation frequency”). In embodiments, the second stage has a gain of 1.

In the illustrated example, a coupling capacitor C4 may act to filter some low- frequency components from the amplifying arrangement, and another capacitor C6 may act to filter some high-frequency components from the amplified modulated signal. Other methods and component arrangements of appropriately filtering the (amplified) modulated signal to thereby apply a band-pass filter on the modulated signal during amplification will be readily apparent to the skilled person.

In this way, the amplifying arrangement may filter and amplify the modulated signal to output an amplified modulated signal within a narrow range of frequencies. It is particularly advantageous to use a cascading set of two operational amplifiers Ul, U2, due to the typically large gain desired for amplifying an input signal, e.g. if the input signal Si_n is of a low amplitude/magnitude. However, any number of operational amplifiers (i.e. at least one) may be used in some other embodiments.

The amplifying arrangement 60 may further comprise a first low-pass filter 61 to remove high frequency content from the modulator output (i.e. the modulated signal) prior to amplification. This can help reduce noise in the amplified modulated signal s_a. Here, the low-pass filter 61 comprises a passive low-pass filter formed of a resistor-capacitor pair R3, C3 that couples high-frequency components to a ground voltage as is well known in the art.

The cut-off frequency of the first low-pass filed 61 can be determined by various implementation requirements, such as the value of the first frequency, expected higher frequencies not of interest, such as those introduced in the input signal and

disturbances, desired roll-off steepness of the low-pass filter and filter design details.

As previously explained, the biasing arrangement is adapted to offset a voltage of the modulated signal to account for a voltage offset introduced in the samples of the amplified modulated signal by the modulating of the input signal.

The biasing arrangement 5 may perform the voltage offset by controlling an input reference voltage to one of the at least two operational amplifiers Ul, U2, as illustrated. In other words, a biasing signal S_bias may be provided to an input terminal of an operational amplifier to thereby bias a magnitude of the modulated signal.

In the illustrated example, a negative terminal of a first operational amplifier Ul is adapted to receive the modulated signal s_mod from the modulating arrangement and a positive terminal of the first operational amplifier Ul is adapted to receive the biasing signal S_bias from the biasing arrangement 5.

The amplifying arrangement may further comprise a second low-pass filter 62 to remove high frequency content from the input signal Si_n prior to modulating by the modulating arrangement 2. This helps further reduce noise. Preferably, the cutoff frequency of the second low-pass is below the modulating frequency of the modulating arrangement, as this allows noise reduction of the input signal that could not be possible after modulating the input signal (i.e. as this would entirely filter the modulated signal). As before, the second-low pass filter may comprise a simple passive filter formed of a resistor-capacitor pair Rl, Cl.

Figure 7 illustrates an operation of the amplifying arrangement according to another embodiment of the invention, and in particular, an operation of the analogue-to- digital converter according to an embodiment. Figure 7 illustrates a sampling signal s_Sam_P (indicating the times at which the analogue-to-digital converter samples the amplified modulated signal), the amplified modulated signal s_a and the input signal Si_n. For the sake of clarity, the amplified modulated signal s_a and the input signal Si_n have been illustrated as being in-phase, although these signals may actually be out of phase (e.g. due to a transfer function of the amplifying circuit).

As before, the analogue-to-digital converter performs a first sampling process in which the amplified modulated signal s_a is sampled at the modulating frequency and synchronized with portions of the amplified modulated signal s_a corresponding to

amplifications of the input signal Si_n. Thus, the first sampling process comprises taking a single sample each period of the amplified modulated signal s_a. Examples of timestamps for samples taken during the first sampling process are shown as“first samples” 71. As the first samples 71 are amplified samples of the input signal, they can be named“first amplified samples”.

The analogue-to-digital converter can be adapted so that it performs a second sampling process or operation. The second sampling operation comprises sampling the amplified modulated signal s_a, at the modulating frequency and synchronized with portions of the amplified modulated signal s_a corresponding to amplifications of the reference voltage level (i.e. and not the amplifications of the input signal). Thus, the analogue-to-digital converter may sample the amplified modulated signal at double the sampling frequency, wherein the sampling alternates between a first sample in phase and a second sample out of phase with portions of the amplified modulated signal corresponding to amplifications of the input signal.

It will be appreciated that the phase difference (or period) between the first samples and the second samples may depend upon a duty cycle of the modulated signal. For example, where the modulated signal has a duty cycle of 50%, the second samples may be 180° out of phase with the first samples. Preferably, the second samples are taken at turning points of the amplified sampling signal (in the portions corresponding to the reference voltage level).

Samples taken during the second sampling process/operation are illustrated as “second samples” 72. The second samples can also be considered to be amplified samples of the input signal, or“second amplified samples”.

Thus, when performing the first and second sampling operations, the analogue-to-digital converter performs two samples 71, 72 for every period of the amplified modulated signal s_a. The two samples may be appropriately spaced within each period of the amplified modulated signal to take a first sample from a portion corresponding to the input signal and a second sample from a portion corresponding to the reference voltage level.

Where the duty cycle of the modulated signal is 50%, the second sample 72 (for the second process) of any given period may be positioned midway between a first sample 71 of the given period and a first sample 71 of an immediately previous/subsequent period. Thus, the second samples may be located halfway between consecutive first samples. In other words, the amplified modulated signal may be sampled at double the modulating frequency, where the sampling generates alternating first and second samples.

In particular, within a single period of an amplified modulated signal s_a, two samples are taken. Preferably, these samples are taken at both turning points within the period (i.e. at a maximum and a minimum). This maximizes an effective gain of the amplifying arrangement.

A difference between the first and second samples can be calculated to generate an amplified sample of the input signal - a“third amplified sample”.

It has been herein recognized that when the amplifying arrangement has applied a low-pass or band-pass filter to the modulated signal or the amplified modulated signal prior to sampling, this results in the (filtered) amplified modulated signal having signal information of the input signal Si_n twice during a single modulating cycle period (i.e. twice within one period of the amplified modulated signal). In other words, information of the input signal is superimpose into the portion of the amplified modulated signal corresponding to the reference voltage level.

As previously explained, the low-pass or band-pass filtering may, for example, be purposively built-in to the amplifying arrangement, in particular the amplifying circuit. In this way, the effective resolution or gain of the amplifying arrangement is increased by a factor of 2, because of the oversampling process. An additional benefit of the proposed methodology is in reducing uncorrelated noise.

Thus, the analogue-to-digital converter may be adapted to determine a difference between each first amplified samples of the input signal and an immediately preceding or following second amplified samples of the input signal to derive third amplified samples of the input signal.

The skilled person will appreciate that the concept of double-sampling the amplifying arrangement herein described may be realized independently of a concept of biasing a magnitude of the modulated signal to account for noise introduced by the modulating arrangement. Thus, according to another concept of the invention, there may be provided an amplifying arrangement for amplifying an input signal of a first frequency, wherein the amplifying arrangement comprises: a modulating arrangement adapted to receive the input signal and generate a modulated signal that alternates, at a second frequency, between a current voltage level of the input signal and a reference voltage level, the second frequency being greater than the first frequency; an amplifying circuit adapted to amplify the modulated signal to thereby provide an amplified modulated signal; an analogue-to-digital converter adapted to perform a first sampling operation comprising sampling the amplified modulated signal at the second frequency and in phase with portions of the amplified modulated signal corresponding to amplifications of the input signal, to thereby obtain first amplified samples of the input signal; a filter circuit adapted to apply a low-pass or band-pass filter to the amplified modulated signal or the modulated signal, the low-pass or band-pass filter being adapted to pass the second frequency, wherein the analogue-to-digital converter is further adapted to perform a second sampling operation comprising sampling the amplified modulated signal at the second frequency and synchronized with portions of the amplified modulated signal corresponding to amplifications of the reference voltage level, to thereby obtain second amplified samples of the input signal.

In other words, the analogue-to-digital converter may be adapted to perform a second sampling operation comprising sampling the amplified modulated signal in phase with portions of the amplified modulated signal that do not correspond to the input signal (i.e. that do correspond to the reference voltage signal). In particular, the analogue-to-digital converter may sample the amplified modulated signal (during the“reference voltage level” portions) at a turning point of the amplified modulated signal.

Figure 8 illustrates an amplifying arrangement 80 according to another embodiment of the invention. The amplifying arrangement 80 again comprises a modulating arrangement 2, an amplifying circuit 3, an analogue-to-digital converter 4 and a biasing arrangement 85. The amplifying arrangement 80 differs from previously described amplifying arrangements by way of the construction of the biasing arrangement.

For the sake of clarification, it is noted that the amplifying circuit 3 has a differential input. A negative terminal is adapted to receive the modulated signal s_mod from the modulating arrangement and a positive terminal is adapted to receive a biasing signal S_bias from the biasing arrangement 85. These connections may be reversed. This effectively results in a differential signal, being the signal that is amplified, consisting of a result of subtracting the biasing signal subtracted from the modulated signal (or an inverse thereof). The biasing arrangement 85 generates a biasing signal S_bias that alternates, at the second/modulating frequency, between a (second) reference voltage level V_ref and a third reference voltage level V₂ref, wherein the biasing signal biases a magnitude of the modulated signal. Preferably, as illustrated, the third reference voltage level is equal to the reference voltage level Vref used for the modulating arrangement 2.

The structure of the biasing arrangement is similar to the structure of the modulating arrangement, so that noise introduced by the modulating arrangement 2 into the modulated signal is mirrored by noise introduced by the biasing arrangement 86 into the biasing signal. In this way, the biasing signal comprises noise similar or identical (i.e. in frequency and magnitude) to the noise introduced into the modulated signal by the modulating arrangement.

Preferably, the biasing arrangement is controlled synchronously with the modulating arrangement (i.e. a switching occurs at a same time), this means that the noise of the biasing signal is in phase with the noise of the modulated signal.

The biasing signal can therefore be subtracted from the modulated signal to thereby account for a noise introduced in the modulated signal by the modulating

arrangement. That is, the biasing signal represents the noise introduced in the modulated signal, which is then subtracted from the modulated signal for amplification.

In the illustrated example, the biasing arrangement 85 comprises a first biasing input terminal 85a adapted to receive the first reference voltage level Vref, a second biasing input terminal 85b adapted to receive a second reference voltage level V_2ref, a biasing output terminal 85c, that provides the biasing signal S_bias and biasing switching logic 85d. The biasing switching logic 85d is adapted to alternately connect the biasing output terminal to the first biasing input terminal 85a and then to the second biasing input terminal 85b, analogously to the switching logic 2d of the switching arrangement 2.

Thus, the structure of the biasing arrangement 85 is substantially similar to the switching arrangement. Preferably, the biasing arrangement 85 is formed of identical components to the switching arrangement.

The first predetermined level V_ref may be buffered by a buffer amplifier 89 (e.g. an operational amplifier arranged to have unity gain, i.e. as a voltage follower). This prevents extra leakage currents from affecting the biasing signal Sbias. Optionally, there is also provided an impedance RM (e.g. resistor) adapted to match the input impedance for the input signal Si_n of the input impedance (e.g. the sensor output impedance) in order to improve a similarity between the modulating arrangement 2 and the biasing arrangement 85. The second reference voltage V_2ref may be provided by a second reference voltage generator 86. The second reference voltage generator 86 is adapted to provide an average of the reference voltage level V_ref as the second reference voltage level V_2ref, in a similar manner to the reference voltage generator 6 and may be structured

similarly/identically.

In another example, the second reference voltage V_2ref may be equal to the reference voltage Vref, e.g. by connecting the first biasing input terminal 86a to the second biasing input terminal 86b.

In other words, the biasing arrangement comprises the same structure as the modulating arrangement 2, but is connected to receive a reference voltage level Vref instead of the input signal Si_n.

The biasing switching logic 85d is controlled synchronously with the switching logic 2d of the modulating arrangement 2. This means that a same noise or disturbance is introduced into the biasing signal S_bias by the switching of the biasing arrangement as is introduced into the modulated signal s_mod by the switching of the modulating arrangement. In other words, the switching noise introduced into the biasing signal S_bias tracks or is almost identical to the switching noise introduced into the modulated signal s_mod.

By providing the biasing signal S_bias to a first terminal of a (differential) amplifier circuit 3 and the modulated signal to a second terminal of the amplifier circuit 3, the modulating noise is mitigated in the differential signal amplified by the amplifier circuit.

In this way, the biasing arrangement biases a magnitude of the modulated signal to thereby account for a voltage offset introduced by the modulating arrangement in the first amplified samples. In particular, the biasing arrangement biases a magnitude of the modulated signal to thereby account for an undesirable noise introduced in the modulated signal by the modulating arrangement.

In particular, the biasing signal is subtracted from the modulated signal, or vice versa, resulting in a clean differential signal for amplification by the amplifying circuit, as the disturbance is identical on both signal paths. The extra hardware required to achieve this noise reduction is minimal, as only a (cheap) biasing arrangement and an optional low cost operational amplifier are required.

In a preferred embodiment, the modulating arrangement 2 and the biasing arrangement 85 are proximate to one another on the circuit board, to ensure similar temperatures in both arrangements. In particular, the modulating arrangement 2 and the biasing arrangement 85 are preferably thermally coupled to one another. It has been recognized that the disturbance from the switch parasitics is temperature dependent, so closely positioning the modulating and biasing arrangements means that the amount of charge injection and leakage current induced in the biasing signal S_bias and the modulated signal s_mod can be matched.

In an even more preferred embodiment the modulating arrangement 2 and the biasing arrangement 85 are combined in the same package. This helps further ensure that the temperature of the two arrangements are equal and that the amount of charge injection and leakage current is matched.

In some embodiments, the amplifying arrangement further comprises a same circuit structure (i.e. type and number of components, such as filters and buffers) between the switching arrangement and the amplifying arrangement as between the biasing arrangement and the amplifying arrangement. This ensures that the biasing signal S_bias is subject to a same noise as the modulated signal s_mod, thereby increasing a noise reduction.

The skilled person will be readily able to derive a method of amplifying an input signal based on any above described amplifying arrangement. That is, each aspect of the amplifying arrangement may be represented as a step in a method of amplifying an input signal.

For the sake of improved clarity, Figure 9 illustrates a flow chart summarizing a method according to an embodiment of the invention. The method 90 comprises a step 91 of receiving the input signal and generating a modulated signal that alternates between a current voltage level of the input signal and a reference voltage level at a second frequency, the second frequency being greater than the first frequency.

The method then moves to a step 92 of amplifying, using an amplifying circuit, the modulated signal to thereby provide an amplified modulated signal.

Subsequently, there is a step 93 of performing a first sampling operation comprising sampling the amplified modulated signal at the second frequency and in phase with portions of the amplified modulated signal corresponding to amplifications of the input signal, to thereby obtain first amplified samples of the input signal.

Following this, the method moves to a step 94 of biasing a magnitude of the modulated signal to thereby account for a voltage offset introduced at the second frequency in the portions of the modulated signal corresponding to the input signal by the generating of the modulated signal. Figure 10 illustrates a sensing arrangement 100 according to an embodiment of the invention.

The sensing arrangement 100 comprises a transmission circuit 101 adapted to transmit an electromagnetic wave l09a. Preferably, the electromagnetic wave l09a is a radio frequency electromagnetic wave.

The sensing arrangement also comprises a sensing circuit 102 adapted to receive a reflection l09b of the transmitted electromagnetic wave and determine a difference in frequency between the transmitted electromagnetic wave and the reflection of the transmitted electromagnetic wave.

The sensing circuit 102 is adapted to output a sensing signal having a frequency equal to the difference in frequency.

Thus, the transmission circuit and sensing circuit can act as a motion detection system or a Doppler detection system, which detects motion based on the Doppler Effect.

The principle of the Doppler Effect is well known: when electromagnetic waves l09a are transmitted towards a moving object 105, then the reflected waves l09b undergo a translation in their frequency. This translation amount is directly proportional to the speed of the object as well as the frequency of the transmitter. Thus, the presence of a translation in the reflected waves is indicative of motion in the vicinity of the sensing arrangement.

The offset in frequency, caused by reflection from a moving object, can be measured by the sensing circuit, according to well-known principles. Subsequently, this measured frequency offset forms the basis of information regarding the speed of the object and leads to motion sensing. This offset frequency is typically made available in the form of a sensing signal, which is a signal alternating at the“Intermediate Frequency” - being the difference between the frequency of the transmitted electromagnetic wave and the reflected electromagnetic wave.

The sensing arrangement further comprises any previously described amplifying arrangement 1, 60, 80. The amplifying arrangement 1, 60, 80 receives, as the input signal, the sensing signal output by the sensing circuit 102.

For typical transmitted frequencies that are used in Doppler detection systems and for typical speed of human motion, this frequency of the sensing signal is between 1 and 500Hz. As previously described, it is difficult to process and amplify such low frequencies, due to l/f noise, large component sizes, susceptibility to distortion from mains (50/60Hz and their harmonics), and susceptibility to vibration, thermocouple effects and microphonic pickup. Moreover, the received signal strength of the reflected electromagnetic wave, and therefore sensing signal, is usually very weak. The received power of the reflected signal is typically in the order of nanowatts hence the output of the sensing arrangement is preferably amplified by 50~80dB or more. The combination of high amplification while avoiding l/f noise and the other noise sources mentioned before at low cost can be extremely challenging. However, the above-described embodiments provide suitable amplifiers for amplifying the low-power, low-frequency sensing signal of such sensing arrangements.

The transmission circuit 101 and the sensing circuit 102 together form a sensing module 101, 102. However, other sensing modules could be employed by the skilled person.

In some embodiments, the sensing arrangement 80 further comprises a switching arrangement 83 adapted to selectively provide power VDD to at least the sensing circuit (or the overall sensing module). In other words, the power supply VDD to the sensing module 81 , 82 may be pulsed. The frequency of the pulsing may be identical, and in phase with the switching frequency s_s. This reduces power consumption of the sensing arrangement 80. Power consumption can be further reduced by reducing a duty cycle of the modulated signal.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a” or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless

telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An amplifying arrangement for amplifying an input signal of a first frequency, the amplifying arrangement comprising:

a modulating arrangement adapted to receive the input signal and generate a modulated signal that alternates, at a second frequency, between a current voltage level of the input signal and a reference voltage level, the second frequency being greater than the first frequency;

an amplifying circuit adapted to amplify the modulated signal to thereby provide an amplified modulated signal;

an analogue-to-digital converter adapted to perform a first sampling operation comprising sampling the amplified modulated signal at the second frequency and in phase with portions of the amplified modulated signal corresponding to amplifications of the input signal, to thereby obtain first amplified samples of the input signal; and

a biasing arrangement adapted to bias a magnitude of the modulated signal to thereby account for a voltage offset introduced by the modulating arrangement in the first amplified samples by providing a current to an input of the amplifying circuit,

wherein the amplifying arrangement applies a low-pass filter or band-pass filter to the modulated signal or the amplified modulated signal, the low-pass or band-pass filter being adapted to pass the second frequency; and

the analogue-to-digital converter is adapted to perform a second sampling operation comprising sampling the amplified modulated signal at the second frequency and synchronized with portions of the amplified modulated signal corresponding to

amplifications of the reference voltage level, to thereby obtain second amplified samples of the input signal.

2. The amplifying arrangement of claim 1, wherein the biasing arrangement is adapted to bias a magnitude of the modulated signal based on magnitudes of the first amplified samples of the input signal obtained by the analogue-to-digital converter.

3. The amplifying arrangement of claim 2, wherein the biasing arrangement is adapted to determine an average magnitude of the first amplified samples of the input signal and bias the magnitude of the modulated signal for the amplifying circuit based on the average magnitude of the first amplified samples of the input signal.

4. The amplifying arrangement of claim 3, wherein the biasing arrangement is further adapted to determine a quiescent voltage of the amplifying circuit and bias the magnitude of the modulated signal for the amplifying circuit based on a difference between the quiescent voltage of the amplifying circuit and the average magnitude of the first amplified samples of the input signal.

5. The amplifying arrangement of claim 4, wherein the biasing arrangement is adapted to bias the magnitude of the modulated signal by a difference between the quiescent voltage of the amplifying circuit and the average magnitude of the first amplified samples of the input signal, so that an average of future first amplified samples of the input signal is approximately the same magnitude as the quiescent voltage of the amplifying circuit.

6. The amplifying arrangement of claim 1, wherein the biasing arrangement is adapted to generate a biasing signal that alternates, at the second frequency, between a second reference voltage level and a third reference voltage level, wherein the biasing signal is used to bias a magnitude of the modulated signal.

7. The amplifying arrangement of any of claims 1 to 6, wherein the reference voltage level is an average of the input signal.

8. The amplifying arrangement of any claim of claims 1 to 7, wherein the modulating arrangement comprises:

a first modulating input terminal adapted to receive the input signal;

a second modulating input terminal adapted to receive the reference voltage level;

a modulating output terminal; and

switching logic adapted to alternately connect, at the second frequency the modulating output terminal to the first modulating input terminal and the second modulating input terminal, to thereby generate the modulated signal on the modulating output terminal.

9. The amplifying arrangement of claim 8, further comprising a reference voltage level generator formed of:

a capacitor connected between the second modulating input terminal and a ground voltage; and

a resistor connected between the modulating output terminal and the second modulating input terminal, so that a voltage level at the second modulating input terminal is held at an average of the input signal.

10. The amplifying arrangement of claim 1, wherein the analogue-to-digital converter is adapted to determine a difference between each first amplified sample of the input signal and an immediately preceding or following second amplified sample of the input signal to thereby derive third amplified samples of the input signal.

11. A sensing arrangement comprising:

a transmission circuit adapted to transmit an electromagnetic wave;

a sensing circuit adapted to:

receive a reflection of the transmitted electromagnetic wave;

determine a difference in frequency between the transmitted electromagnetic wave and the reflection of the transmitted electromagnetic wave; and

output a sensing signal having a frequency equal to the difference in frequency; and

an amplifying arrangement according to any of claims 1 to 10, wherein the sensing signal output by the sensing circuit is received as the input signal.

12. A method for amplifying an input signal of a first frequency, the method comprising:

receiving the input signal and generating a modulated signal that alternates between a current voltage level of the input signal and a reference voltage level at a second frequency, the second frequency being greater than the first frequency;

amplifying, using an amplifying circuit, the modulated signal to thereby provide an amplified modulated signal;

performing a first sampling operation comprising sampling the amplified modulated signal at the second frequency and in phase with portions of the amplified modulated signal corresponding to amplifications of the input signal, to thereby obtain first amplified samples of the input signal; and

biasing a magnitude of the modulated signal to thereby account for a voltage offset introduced at the second frequency in the portions of the modulated signal

corresponding to the input signal by the generating of the modulated signal.

13. The method of claim 12, wherein the step of biasing comprising biasing the magnitude of the modulated signal for amplification based on the first amplified samples of the input signal obtained by the analogue-to-digital converter.

14. The method of claim 13, wherein the step of biasing comprises:

determining an average magnitude of the first amplified samples of the input signal;

determining a quiescent voltage of the amplifying circuit; and biasing the magnitude of the modulated signal for amplification based on a difference between the quiescent voltage of the amplifying circuit and the average magnitude of the first amplified samples of the input signal.