KR20050024398A - Automatic frequency control receiver - Google Patents

Abstract

The present invention relates to a receiver for a signal S received on a wireless network operating at a reference oscillation frequency controlled by a reference value Vref. The receiver comprises demodulation means DEMO for demodulating the received signal S, estimation means EST for estimating an average value MV of the demodulated signal SD, and the average value MV of the demodulated signal SD with respect to the reference value Vref. Correction means COR for correcting and determining means DEC for determining the binary value taken by the received signal S. According to the invention, said estimating means EST comprises: first means ESTA for rapidly extracting a first average value MVA of said demodulated signal SD used in said determining means DEC for a first period, and said correcting means for a second period of time; A second means ESTB for extracting at low speed a second average value MVB of the demodulated signal SD used in COR and determining means DEC.

Description

Receiver, signal receiving and processing method, integrated circuit {AUTOMATIC FREQUENCY CONTROL RECEIVER}

TECHNICAL FIELD The present invention relates to a wireless receiver, and more particularly, to a method for removing a frequency difference typically detected in a signal received by a wireless receiver between a local frequency of a receiver and a local frequency of a received signal.

For example, in the Bluetooth standard, the receiver must be able to handle large frequency differences. In a wireless system comprising a transmitter in communication with a receiver, there is generally a difference between the frequency of the transmitter and the frequency at which the local oscillator of the receiver operates, ie the reference frequency. This frequency difference is evident by the voltage difference at the output of the demodulator of the receiver. It is already known how to analyze the demodulated signal over a period of time to remove this voltage difference and then to remove the voltage difference from the signal or to use the voltage difference to adjust the local oscillator in an automatic frequency control loop (AFC loop). Known. Therefore, in this prior art, a radio receiver operating at a so-called reference oscillation frequency controlled by a so-called reference value includes demodulation means for demodulating a received signal, means for estimating an average value of the demodulated signal, and an average value of the demodulated signal. Means for correcting for a reference value and determining means for determining a binary value taken by the received signal.

The function of correcting the average value of the signal demodulated by the automatic frequency control loop is already known. In such a loop, the estimating means for estimating the voltage difference comprises, for example, passing the demodulated signal through a low pass filter having a narrow passband that eliminates useful signals and preserves continuous components.

The present invention includes the following considerations.

The choice of passband for the lowpass filter is a compromise, in which the method slows down to remove the continuous components and if the passband widens to increase the operating speed, then the estimation of the continuous components is performed on the filter. It is confused by the components of the signal passing through it. The disadvantage of this low speed method is that most of the signal is required to estimate the voltage difference before the reception of useful information, which is time consuming and degrades the accuracy of detecting each start point of the reception range. However, a disadvantage of the method of making fast but continuous component estimation difficult is that an error is introduced into the received signal by the method of estimating the voltage difference.

Summary of the Invention

It is an object of the present invention to make it possible to obtain a receiver for a signal received over a wireless network and generally by various reception ranges which does not have the disadvantages of the prior art.

To this end, the radio receiver mentioned at the outset is characterized in accordance with the present invention that the means for estimating, according to the invention, the first means for quickly extracting the first average value of the demodulated signal used in the determining means for the first period and the correction means for the second period. And second means for extracting at low speed a second average value of the demodulated signal used in the determining means.

These two types of mean estimating means are complementary, so that most of the signal is used for estimating the mean value so that the system does not slow down or incorrectly estimate the mean value of the signal. The signal receiving circuit thus obtained can combine frequency low speed estimation and high speed estimation to simultaneously achieve good sensitivity of the receiver and accurate correction of frequency from the start of the reception range.

In particular, in an embodiment of the invention, the means for correcting the average value of the demodulated signal uses a frequency correction loop. The principle of automatic frequency control is known for analog data and digital data.

In an advantageous embodiment of the invention, the first estimating means comprises means for estimating the minimum and maximum values of the received signal and estimating the mean value of the signal at an intermediate value between these two values. This estimation is quick. However, this estimation method is relatively inaccurate. For example, if a series of consecutive 1s or 0s are present in the signal. This estimation can be used for the entire signal but the accuracy of the determining means is affected.

Thus, in the preferred embodiment of the present invention, in the received signal composed of the synchronizer, the controller and the data portion, the first period does not exceed the period required for the reception of the synchronizer and the controller.

The present invention can be implemented in any receiver operating on a wireless network where significant frequency differences occur. Bluetooth, DECT technology and any other technology that provide the above-mentioned characteristics are related.

The principle according to the invention can be used well in digital data or analog data.

The invention also relates to an integrated circuit in which the receiver according to the invention is present.

The invention also relates to a method for receiving and processing a signal received from a wireless network according to the invention.

The invention will be described by the embodiments described with reference to the drawings, but these embodiments do not limit the invention.

1 is a block diagram of a receiver in accordance with the present invention;

2 is a block diagram of a general principle of an automatic frequency control loop,

3 is a diagram of an embodiment of an amplifier implemented within a frequency control loop,

4 is a functional diagram of a receiver according to the invention according to an advantageous embodiment,

5 is a timing diagram for controlling various components of the present invention in accordance with a preferred embodiment of the present invention;

FIG. 6 is a graph showing the results of frequency correction obtained with an implementation of the present invention by a set of curves representing voltages at various points in the circuit of FIG.

Reference is now made to the reference signs. Like elements are denoted by like reference numerals throughout the drawings. Several similar components may appear in a single drawing. In this case, numbers or suffixes are added to the reference signs to distinguish similar components from each other. Such numbers or suffixes may also be omitted for convenience. This also applies to the description part of the invention and the claims.

The following description is provided to enable any person skilled in the art to make or use the present invention. This description is provided by considering the patent application and its necessary compliance. Various alternatives to the preferred embodiments will be apparent to those skilled in the art and the general principles of the invention disclosed herein may be applied to other implementations.

Therefore, the present invention is intended to cover the broad scope consistent with the features and principles described below rather than being limited to the embodiments described above.

1 is a block diagram of a receiver in accordance with the present invention. This figure provides a means for performing the various functions required to implement the invention. These functions are steps in the reception method of the present invention. The receiver according to the invention receives a signal S from a wireless network. The receiver may for example be an antenna and comprises a receiving means not shown. The receiver operates at the so-called reference oscillation frequency, which is controlled by the so-called reference value Vref. This reference value is usually voltage. The receiver according to the present invention comprises a demodulation means DEMO for demodulating the received signal S, an estimating means EST for estimating the average value MV of the demodulated signal SD, and a means for correcting the average value MV of the demodulated signal SD with respect to the reference value Vref. And determining means DEC for determining the binary value taken by the received signal S. According to the invention, the first means ESTA and the correction means COR and the determining means during the second period, wherein the estimating means EST quickly extracts the first mean value MVA of the demodulated signal SD used in the determining means DEC during the first period. Second means ESTB for extracting at low speed the second average value MVB of the demodulated signal SD used in the DEC. The data processed by the receiver according to the invention is analog data or digital data. From now on, it is proposed to use the present invention in analog processing of digital data. Mean value estimating means are used to process analog data. Digital means for estimating digital data can be used without adversely affecting the principles of the present invention.

In the specific embodiment shown in Fig. 1, the correction means COR for correcting the average value MV of the demodulated signal SD is looped onto the demodulator DEMO to form a frequency correction loop. This loop is generally known as an automatic frequency control loop. 2 illustrates the general principle of an automatic frequency control loop. The function of this frequency control loop is doubled. This loop keeps the frequency fIF constant regardless of the frequency difference in the received signal. The loop also compensates for any changes in method and temperature by automatically modifying the frequency fIF to the center frequency of the demodulator. This is accomplished by looping information about the average frequency fIF onto the local oscillator VCO so that the adjustment of the local oscillation frequency fVCO can be made automatically. The output signal of the demodulator DEMO is filtered at low pass filter FIL to extract the average value of the signal frequency. This filter FIL constitutes means ESTB for low speed estimation of the average value MVB of the demodulated signal SD. An example of such a filter is shown in FIG. 4. The mean value MVB is compared to the reference value Vref. This creates an error signal, for example. This information is amplified and provided to the control input of the local oscillator VCO. This changes the VCO frequency to cancel the frequency difference between the signal frequency and the local oscillation frequency.

More precisely, the demodulator has a linear response in the form

SD = Vc-Kd (fIF-fc),

Where Vc is the output voltage when fIF is equal to fc and Kd is the demodulator gain. Voltage SD is available at the output of the demodulator. Demodulator DEMO is followed by means ESTB for estimating the average value MVB of the signal SD. This estimating means ESTB is advantageously composed of the low pass filtering means FIL as described above. The obtained average value MVB is proportional to the frequency difference between the frequencies fIF and fc. Next, the average value MVB is compared with the reference value Vref and the result is amplified by the amplifying means AMP having gain A and applied to the local oscillator VCO of the receiver. This is summarized as follows.

Vmod = Vref + A (Vin-Vref)

The output signal of the amplifier AMP is applied to a local oscillator VCO operating at frequency fIF. Thus, the following equation holds.

fVCO = fref + Km (Vmod-Vref),

Where fref is the frequency when Vmod is equal to Vref and Km is the modulation gain. Each signal frequency difference modifies the current frequency fIF of the same value in the opposite direction. And the following equation holds.

fIF = fVCO-ΔfRF

Next, the system's response to the change in frequency RF may be the carrier frequency difference or the modulation itself.

Using the previous equation, the following expression is finally obtained.

Here, if Vc = Vref, the equation is simplified as follows.

Ideally, this system is configured such that fc = fref. In other words, this means that when fIF = fref, the output voltage Vc = Vref. For example, due to a change in method, this may not be the case. If the frequency difference [Delta] fRF of the signal is zero and the loop gain KmAFKd is very large, this equation seems to shift the center of frequency fIF such that fIF = fc.

If there is a frequency difference in the received signal, this loop will bring the frequency fIF close to fc because the voltage difference is attenuated by a factor of 1 + KmAFKd.

The loop must compensate for any slow drift in the frequency of the received signal but not respond to its modulation. This is accomplished by optimization of the loop filter.

If you choose the first order filter to have the transfer function

In the case of fc = fref, the following equation is obtained.

Where Gloop = KmAF (0) Kd is the static loop gain.

For a received signal that changes so rapidly that the loop does not respond, the modulation is delivered without attenuation within the loop. The loop amplifier must have a high input impedance to be sensitive to the voltage present on the loop filter capacitor. Its output controls the tuning of the local oscillator VCO. The amplifier is implemented according to FIG. 3, for example by a transconductance type amplifier with a return.

The loop amplifier can be divided into the following gain terms Gv and return gain terms β.

The closed loop gain is

For example, about 20 gains are required in certain applications. Since the transconductance is an amplifier with one stage, the gain is not very large and the desired gain is achieved with a very low return value (Gvβ slightly larger than 1). Here, let's look at the general operation of the automatic frequency control loop. In an application to a receiver operating on a wireless network, such as a Bluetooth receiver, for example, a determination means DEC is needed to determine whether a signal corresponds to 1 or 0, ie to determine the binary value of the received signal. The automatic frequency control loop and the determining means DEC require extracting the average value of the signal but have different requirements for this extraction. In the case of the determining means DEC, the extraction should be fast during the start of the receiver's reception range. The beginning of this reception range generally corresponds to the access code and signal synchronization and error control signals. On the other hand, in the case of a frequency control loop, slow extraction is required permanently to prevent attenuation or cancellation of the modulation by the frequency control loop. During the start of the reception range, the extraction of consecutive components is preferably carried out by the first means ESTA to extract the mean value. Thus, this loop has a low gain (eg 6). The period during which extraction is performed by various means EST for estimating the mean value MV is selected according to the characteristics of the signal to be received by the receiver. In FIG. 4, this period is controlled by the control means which is a switch controlled according to the timing diagram shown in FIG. 5, for example.

4 shows an advantageous embodiment according to the invention. The means shown in FIG. 1 are described in detail in the context of analog processing of data.

In Fig. 4, the receiver receives signal S at its demodulation means DEMO. The demodulation means operates the switch R_ON to put the system in the data receiving state. Once demodulation has been performed, the demodulated signal SD is provided to the input of two kinds of means ESTA, ESTB for estimating the mean values MVA, MVB. The first means ESTA is high speed and this means estimates the maximum and minimum values of the signal and takes the median of these two values as the average value of the demodulated signal SD. An implementation for this estimation is shown in FIG. 4. Limit value estimation and median value calculation of the signal as shown in FIG. 4 are not described any further because they are well known in the art. The second means ESTB consists of a low pass filter R2C1, for example according to FIG. 4. The value of capacitor C1 is selected from a compromise on the time constant of the RC filter called ESTB. This value is typically high and the capacitor is an external capacitor. The time constant should be very long in order to better estimate the average value of the output signal of the demodulation means, but when the reference input of the determining means is switched to the output of the low speed RC filter, the filter output level is already selected at its end value at the end of the access code. It should be very short so that The present invention requires only one external capacitor in the circuit, thereby reducing receiver manufacturing time and manufacturing space. This single outer capacitor is used permanently in the frequency control loop and for a fixed period of time for the determining means.

The correction means comprises an amplifier AFC connected to the input of the local oscillator VCO in the same manner as shown in Fig. 2, the entire part of which is arranged in a loop with the demodulation means DEMO. The determining means DEC comprises an amplifying element SLI for fixing the output value to 0 or 1 in accordance with two inputs, the first of the two inputs receiving an average value of the signal input from one of the estimating means ESTA, ESTB. And the second input receives the demodulated signal SD itself. Advantageously, this amplifying element SLI also deactivates the switch signal R_ON activated by the demodulation means DEMO in the absence of any signal to be processed. According to a preferred embodiment, various switches are operated according to the timing diagram shown in FIG.

Before the reception range begins, that is, before powering up the receiver in FIG. 5, the external capacitor C1 is precharged to the reference voltage by activating the switch signal S_EN shown on the first line of the timing diagram of FIG. 5. Now when the receiver powers up, the local oscillator VCO and loop PLL are started. At the beginning of the reception range, the detection of the signal is indicated to all components of the receiver by the signal R_ON triggered by the demodulation means DEMO. Receive REC starts and data DATA arrives in the form shown in FIG. These data constituting the received signal are formed of an access code consisting of synchronization and error check elements PR, SYN, TR, and a specific data packet PAYL, which is data specific for the communication that is subsequently processed by the receiver. The switch signal R_ON now switches the external capacitor C1 onto the output of the demodulation means DEMO for the next estimation of the mean value MVB of the signal by the second estimating means ESTB. Relatively long time constants are used. In the case of a frequency difference, the mean value MVB of the signal is different from the reference frequency Vref. This information is provided at the input of the oscillator VCO to calibrate the receiver's frequency. This forms an automatic frequency control loop. During this time, the receiver must determine whether the received bit is zero or one. This should be done by comparison with the mean value MV of the signal. The mean value MVB provided by the estimating means ESTB is used at the beginning of the reception range because this mean value does not converge quickly enough to the actual mean value. Therefore, other circuits are used. This circuit comprises estimating means ESTA for determining an average value from detection of the peak. This estimation means ESTA is reinitialized by activating the switch SR. Detection of peaks and estimation of peak value MIMA are performed during the time constant shown in FIG. During this estimation, switch S2 is activated and switch S3 is opened so that the average value of this signal is available at the output of the estimation means ESTA and at the reference input of the determining element SLI. Next, by opening the switch S2 and closing the switch S3, the reference input of the determining means DEC is switched to the average value MVB measured by the estimating means ESTB. The frequency control loop and the determining means then use the same average value MVB of the signal. The time constant is selected such that this switching can occur before the arrival of the data packet PAYL, which contains the specific data of the communication being processed next by the receiver.

The simulation was performed with the various components of FIG. 4 as suggested values in the table below. This simulation result is proposed in FIG.

These values are given by indications and do not exclude other values. For example, the external capacitor C1 adjusts the average value to a reference value in a particular application and increases with longer time constants for acquiring data. The simulation was performed for a carrier frequency difference of, for example, about 100 KHz (200 KHz in FIG. 6). In this simulation, for example, the operations performed on the timing diagram of FIG. 5 are found. The loop PLL and frequency control loop are activated first. The frequency control loop is initialized with the same reference voltage Vref of 1.45 volts as used for the local oscillator. After the loop PLL is set to the desired frequency, the receiver is activated at 200 Hz according to the timing diagram of FIG. Data arrives on curve Demod_OUT at 225 ms. In FIG. 6, these data are charged on the external capacitor C1 and have a difference to the reference voltage Vref indicated by the curve C ext. By the present invention, in the simulation, the effect of the demodulated curve Demod_OUT and the frequency control loop to recover the data is observed around the Vref represented by the curve C ext (Vin AFC). The average voltage used by the determining means indicated on the curve DC_Slicer is first of all provided to the estimating means by the detection of the peak on the curve Demod_OUT, which means for estimating the header packet of the data packet at approximately 350 Hz in FIGS. 5 and 6. And on access code. At this moment, the frequency control loop corrects the initial frequency difference. The continuous component level MVA estimated by the estimation means ESTA by peak detection is close to the average level MVB indicated by the external capacitor C1. The reference input of the determining means is switched to the external capacitor C1.

Although the invention has been described with reference to the described embodiments, those skilled in the art will understand that various modifications and changes can be made within the spirit and scope of the invention. Such modifications and variations are not to be excluded within the spirit and scope as defined in the following claims.

Claims (7)

A receiver for a signal received on a wireless network, operating at a reference oscillation frequency controlled by a reference value, the receiver comprising: Demodulation means for demodulating the received signal; Estimation means for estimating an average value of the demodulated signal; Correction means for correcting the average value of the demodulated signal with respect to the reference value;  Determining means for determining a binary value taken by the received signal, The estimating means, First means for rapidly extracting a first average value of the demodulated signal used in the determining means for a first period of time, Second means for extracting at a low speed a second average value of the demodulated signal used in said correction means and said determining means for a second period of time; receiving set. The method of claim 1, The correction means for correcting the average value of the demodulated signal uses a frequency correction loop. receiving set. The method according to claim 1 or 2, The second extraction means comprises low pass filtering means for extracting an average frequency of the signal. receiving set. The method according to any one of claims 1 to 3, The first extracting means includes means for estimating a maximum value and a minimum value of the received signal and estimating an intermediate value between the maximum value and the minimum value as an average value of the received signal. receiving set. The method according to any one of claims 1 to 4, The received signal consists of a synchronization part, a control part and a data part, The first period of time does not exceed the period required to receive the synchronization portion and the control portion. receiving set. An integrated circuit comprising a receiver according to any one of the preceding claims. A method of receiving and processing a signal received via a wireless network, Demodulating the received signal; Estimating an average value of the demodulated signal; A correction step of correcting the average value of the demodulated signal with respect to a reference value; A determining step of determining a binary value taken by said received signal, The estimating step, A first step of rapidly extracting a first average value of the demodulated signal used in the determining step for a first period of time, A second step of slowly extracting a second average value of the demodulated signal used in the correction step and the determining step for a second period of time; How to receive and process a signal.