DE10351699B3 - Local oscillator signal generator for radio terminal, e.g. mobile phone, uses CMOS switch to generate amplitude-controlled I and Q signals from RC-CR filter - Google Patents

Abstract

An RC-CR filter is placed after a signal generator (VCO), and two limiter amplifiers (V1,V2) control the amplitude of two signals from the filter. A first CMOS transistor switch controls theses signals so that there is no fundamental-frequency superposition. Thus a first waveform (E1) is generated in which a sine wave follows a cosine wave, and a second waveform is generated in which a sine wave follows and inverted cosine wave. An independent claim is included for a mobile terminal device.

Description

The The present invention relates to an apparatus for generating Local oscillator signals (LO) whose I and Q components have a phase difference of 90 ° over the entire bandwidth.

devices of the type mentioned can et al in communication devices according to the GSM (Global System for Mobile Communications) and UMTS (Unified Mobile Telecommunications System) standard application.

In Communication systems are complex converters or mixers used, which over an internal circuit suppressing mirror signals. This will be complex I and Q signals (real and imaginary part) formed orthogonal are, i. stand vertically. Are by mixing or scanning superimposed the I and Q signals, so there is no mutual influence, because at ideal Phase difference of 90 ° none I component exists on the Q path or Q component on the I path.

at The mobile radio standards GSM and UMTS, for example, blockers lie in mirror band with high level, while at the same time the useful signal the standards have an extremely low level. It exists the danger that the blocker signal in the Nutzfrequenzband with the actual useful signal already at low phase deviation of just a few degrees can, in addition the level of the blocker signal is greater than is the level of the useful signal to be processed.

Basically the requirements for external filters for mirror suppression the lower the better the internal mirror suppression works. Because the communication bands for mobile Communication systems the frequency range from 600 MHz to 2.4 GHz are the requirements for the local oscillator signals in terms of their phase error correspondingly large.

One measure of mirror suppression is the so-called Image Rejection Ratio (IRR), which is expressed in dB. The following relationship between phase errors in degrees and IRR results:

at known systems were given with phase errors of 3 ° to maximum 10 ° satisfied. The problem was due to higher Requirements for analog high frequency filtering, analogue Wiring and the chipset solved.

For future applications however, the phase error should be less than 0.5 °.

From the document DE 600 02 275 T2 For example, there is known a quadrature signal generation system used for generating two carrier signals with an accurate quadrature ratio for a quadrature modulation and demodulation mirror selection frequency converter in a radio communication.

Consequently It is an object of the present invention to provide a device of to provide the aforementioned type, which provides better mirror suppression.

These The object is achieved by the device having the features of the claim 1 solved. Advantageous developments of the invention will become apparent from the dependent Claims.

The inventive device for generating local oscillator signals (LO), whose I and Q components have a phase difference of 90 ° over the entire bandwidth, comprises means for Generating an input signal, in particular a signal generator, an RC-CR filter circuit downstream of the means for generating the input signal, which generates a first and a second signal, and at least two limiter amplifiers for amplitude control of the first and the second signal.

According to the invention switch first switching means, in particular CMOS transistors, the first and the second amplitude-controlled signal in such a way that no fundamental wave overlays occur. In this way, there is an advantageous mirror suppression.

Further a first waveform is generated with the aid of the first switching means, in which a sine wave follows a cosine wave, and a second waveform in which a sine wave is an inverted one Cosine oscillation follows.

Further preferably shorten second switching means, in particular switched capacitance filters or tact switch, the first and the second signal, allowing one first and a second modified signal is formed.

In an advantageous embodiment become the positive edges of the first and second signals as switching edges for generating the first and the second modified Used signal.

In a further embodiment is a third modified signal by inverting the second modified Signals generated.

Advantageous may be the first modified signal with the third modified Signal, and the first modified signal with the second modified Signal are connected in time.

Prefers is the first switching means suitable to perform temporal interconnection.

In another embodiment, orthogonal harmonic sets are generated for the frequencies f = (2n + 1) * 2 * f ₀ , where f _{0 is} the frequency of a cosine or sine section and n is an even number.

Advantageous in the present invention, the first and the second Signal can be out of sync with each other in time, but the signals have to be periodic consequences the harmonics of the two signals to each other but still orthogonal are.

In a final embodiment can be a higher one Frequency band by multiplying the second signal, in particular of a cosine signal to be covered with the local oscillator signal.

The The present invention also relates to a mobile terminal, in particular a mobile device, which is a device according to the invention having.

The The invention is described below with reference to the accompanying drawings based on several embodiments explained in more detail. The features shown there and also those already described above Features can not only in the combination mentioned, but also individually or be essential to the invention in other combinations. Show it:

1a an RC-CR filter circuit,

1b the output signals over the time of the circuit according to 1a .

2 an addition or subtraction of the signals according to 1b in the complex plane,

3 Signal sequences of sine + cosine signals or sine + inverted cosine signals over time and representations in the complex plane,

4 Simulation results from sine and cosine square wave signals,

5a Amount of sine + cosine signal,

5b Amount of spectrum according to 5a .

5c Phase of the spectrum according to 5a .

6a Waveform of sine + inverted cosine signal,

6b Amount of spectrum according to 6a .

6c Phase of the spectrum according to 6a .

7a modified rectangular form of sine + cosine signal,

7b Amount of spectrum according to 7a .

7c Phase of the spectrum according to 7a .

8a modified rectangular form of sine + inverted cosine signal,

8b Amount of spectrum according to 8a .

8c Phase of the spectrum according to 8a .

9a original sinusoidal signal and modified sinusoidal signal over time,

9b original cosine signal and modified cosine signal over time,

10a Circuit of the modified sine signal,

10b Circuit of the modified cosine signal, and

11 Circuit for generating local oscillator signals.

1a shows an RC-CR filter circuit. A signal generator VCO generates an input signal for the RC-CR filter circuit. The input signal is split into two parallel branches, with a capacitor C1 in a first branch and a resistor R2 in a second branch. The first branch in turn is divided into a parallel connection of a grounded resistor R1 and a limiter amplifier B1. The second branch is divided into a parallel connection of a capacitor C2, which is grounded, and a limiter amplifier B2. The two amplifiers B1 and B2 deliver the signals S1 and S2.

1b shows in each case the amplitudes of the two square-wave signals S1 and S2 over time. In this case S1 corresponds to a sine signal and S2 to a cosine signal.

2 FIG. 12 shows addition (S1 + S2) and subtraction (S1-S2) by the RC-CR filter circuit according to FIG 1a generated signals S1 and S2 in the complex plane. Where I denotes the real part and Q the imaginary part. 2 shows the vectors of the signals S1, S2 and -S2. From the 2 It can be seen that the added signal S1 + S2 with respect to the subtracted signal S1 - S2 has a phase difference of 90 °. The signals S1 and S2 are not synchronous with each other, but have a phase offset ΔΦ. Consequently, all harmonics of the pairs S1 + S2 and S1 - S2 are perpendicular to each other, ie, the pairs are orthogonal to each other. It is advantageous that sine and cosine signals, or their rectangular time functions S1 and S2, need not be in synchronism with one another. It is only necessary that the periods of the signals S1 and S2 are complete. The signal S1 may, for example, have a time offset with respect to the signal S2 or vice versa, but the two signals must have the same period duration.

3 shows two preferred waveforms E1 and E2 in which an orthogonal sequence occurs without disturbing fundamental wave superposition. Where A is the amplitude of the signal and t is the time. In the upper timing diagram, a first waveform consisting of a sine wave followed by a cosine wave is shown. In the timing diagram below, there is shown a second waveform in which an inverted cosine wave follows a sine wave. The graphs (E1 + E2) and subtraction (E1 - E2) of the waveforms E1 and E2, respectively, in the complex plane are shown in the graph to the right of the timing diagrams. The added or subtracted signals are again perpendicular to each other.

4 shows the results of a simulation with the simulo-mathematical simulation program Matlab. The two top diagrams show two square-wave signals s1 (t) and s2 (t). These rectangular sequences, which are offset by approximately 90 ° and which correspond to sine and cosine signals, are added to y1 (t) and subtracted y2 (t). In the penultimate or last diagrams from bottom to top, the Fourier components of the added y1 (t) and subtracted y2 (t) time signals are shown in terms of magnitude and phase. All harmonics of the signals have a phase difference of 90 °, ie they are orthogonal to each other. However, the signals s1 (t) and s2 (t) do not have to be synchronous with each other. One signal may have a time offset from the other, but the sequence must be periodic. For the signals of 4 was calculated with a phase shift of 5 ° between s1 (t) and s2 (t).

The orthogonality of the signals is thus independent of the phase offset. Like from the 2 however, a phase offset causes rotation of the sum vector S1 + S2 in the I / Q plane. It can be seen that an amplitude error occurs, ie the phase error has changed into an amplitude error. However, the amplitude error has little effect, since it is local oscillator frequencies, which on the in 1 limiter amplifiers B1 and B2 shown can be brought to the same amplitude.

This relationship between phase error and amplitude error can be mathematically derived as follows:
It is assumed that two local oscillator signals s _I and s _Q.

The local oscillator signal s _I in the I-path has a fundamental frequency where and has any number of harmonics.

In the Q path, the local oscillator signal s _{Q, which is} phase-shifted by 90 ° relative to the I path, has an additional phase error ΔΦ.

With sin (x) = cos (x - π / 2) follows:

Furthermore, a negated signal of the Q-path s _{QN should} exist:

With -sin (x) = cos (x + n / 2) follows:

For the sum signals s ₁ = s _I + s _Q and s ₂ = s _I + s _QN then applies

From equation (6) it can be seen that the phase shift between the signals s ₁ and s _{2 is} exactly equal to 90 °. However, it can also be seen that only for ΔΦ = 0 are the amplitudes A _{n '} and A _n'' identical. The existing before the summation phase error between the I and Q signal is therefore in an Ampli Tudenfehler has been transformed. To eliminate this error, a subsequent amplitude control or limitation of the sum signals can preferably be used.

One However, problem may arise if the faulty ones and the corrected I / Q signals and their harmonics on top of each other lie, i. the new orthogonal I / Q signals are on it discrete frequencies such as the phase error-prone signals Output variables. By these overlays can disorders occur.

The 5 and 6 Matlab simulations show the addition of sine + cosine signal or sine + inverted cosine signal.

5a shows the rectangular shape of sine + cosine signal and 6a shows the rectangular shape of sine + inverted cosine signal. Accordingly, the show 5b and 5c respectively. 6b and 6c the spectra after a Fourier transform of the signals in magnitude and phase.

The rectangular waveforms corresponding to the sine and cosine signals yield Fourier components only for odd harmonics with (2n + 1) * 2 * f ₀ , ie for 2f ₀ , 6f ₀ , 10f ₀ , etc., where 2f _{0 is} the frequency of the sine wave. or cosine parts of the waveform. However, a fast Fourier transform (FFT) of the combination of sine and cosine signals yields a spectrum with the fundamental at the frequency f ₀ , with the harmonics then at n * f ₀ , ie, f ₀ , 2f ₀ , 3f ₀ , and so on , Since the fundamental wave of the useful signal is at the frequency 2 · f ₀ , a separation of unwanted spectral components is preferably carried out at the system output. The combined waveform and the two individual components (sine or cosine) do not interfere with each other. A possible influence on phase errors of the originally non-orthogonal functions is excluded. The harmonics at the frequencies (2n + 1) * 2 * f ₀ are orthogonal in this case, but the individual sequences need not be synchronous with each other.

7a shows a Matlab simulation of a modified rectangular form of sine + cosine signal.

According to shows 8a a Matlab simulation of a modified rectangular form of sine + inverted cosine signal.

The 7b and 7c respectively. 8b and 8c again show the respective spectra of the signals according to the 7a and 8a by amount and phase.

to A series connection of the modified waveforms can be used CMOS switch (transistor) can be used, which has a certain switching time needed.

Since the waveforms may be phase shifted but must not have any parts swallowed by the switch, the waveforms must be in accordance with the 7 and 8th be changed. It is conceivable, for example, to shorten the rectangular signal corresponding to the cosine, if this contains only cosine components.

The 9a and 9b show the necessary changes to get from a source signal to a modified signal. 9a shows in the upper timing diagram, the amplitude of the rectangular shape of a sine signal over time t. T designates the period duration. From the lower timing diagram, a first modified signal M1 can be seen.

According to shows 9b in the upper time diagram, the amplitude of the rectangular shape of a cosine signal over time. In the lower timing diagram, a second modified signal M2 is shown. The reduction of the amplitude of the two signals for 2 * f ₀ due to the changed time function from 0.45 to 0.225 can be compensated by amplification or by shorter switching times. These shortened sequences can be realized by circuits, for example with switched capacitance filters or clock switches.

The 10a and 10b show how to get from the rectangular shapes of the sine and cosine signals to the modified signals M1 and M2 by appropriate circuit. The amplitude is again denoted by A and the period is T. From the original waveforms SIN the 10a or COS the 10b In each case their positive edges can be used for switching. The trigger pulses are each represented by the arrows TR. In 10a is further the switching time of the cosine signal SZCOS and in 10B the switching time of the sine signal SZSIN drawn.

11 shows a possible realization of a circuit according to the present invention. A signal generator VCO generates an input signal for an RC-CR filter circuit comprising the components R1, C1, R2 and C2. The RC-CR filter circuit supplies a sine or cosine signal via two limiter amplifiers V1 and V2, respectively. In addition, the second output signal of the RC-CR filter circuit before being supplied to the limiter amplifier V2 is supplied in parallel to a further limiter amplifier V3, in which the signal is inverted, so that there is additionally an inverted cosine signal. These signals are correspondingly connected in the manner (not shown in detail), so that the modified square-wave signals M1, M2 and -M2, as shown 11 is apparent receives. These modified waveforms are then connected in series. In this case, a temporal connection of the modified signal -M2 with M1 and the modified signals M1 with M2, so that two modified signal sequences arise, as in the right part of the 11 are shown. For switching, the positive edges of the original waveform, ie of the sine or cosine signal are preferably used.

Around a higher one For example, it is possible to cover a frequency band exactly in quadrature standing I / Q local oscillator signal multiply by a cosine signal. Cos (x) · cos (x) · cos (2x) and cos (x) · sin (x) sin (2x), the result is a useful band with twice the frequency, however without phase error. This process can be continued as desired.

• 1. I/Q-Lokaloszillator-Signale mit geringstem Phasenfehler können erzeugt werden.
• 2. Bei einer Addition und Subtraktion eines einzelnen Sinus- und Kosinussignals sind alle Oberwellen der addierten Signale (S1 + S2) und der subtrahierten Signale (S1 – S2) orthogonal zueinander. Die Signale S1 + S2 und S1 – S2 müssen dabei nicht synchron zueinander sein, d.h. sie können zueinander zeitversetzt sein.
• 3. Die modifizierte Zeitfunktionen S1 + S2 und S1 – S2, wobei S1 und S2 als zeitliche Folgen hintereinander geschrieben werden, liefern orthogonale Oberwellensätze für die Frequenzen f = (2n + 1)·2f₀, wobei f₀ die Frequenz des Kosinus- oder Sinusteilstücks ist.

The present invention has the following significant advantages:

• 1. I / Q local oscillator signals with lowest phase error can be generated.
• 2. In addition and subtraction of a single sine and cosine signal, all harmonics of the added signals (S1 + S2) and the subtracted signals (S1-S2) are orthogonal to each other. The signals S1 + S2 and S1 - S2 do not have to be synchronous with one another, ie they may be offset in time from one another.
• 3. The modified time functions S1 + S2 and S1-S2, wherein S1 and S2 are written consecutively as time sequences, provide orthogonal harmonic sets for the frequencies f = (2n + 1) · 2f ₀ , where f _{0 is} the frequency of the cosine or Sinusteilstücks is.

With the structure of the timing functions shown above, it is possible disturbances the erroneous output signals, i. from the RC-CR generator, Completely to suppress.

Claims (10)

Device for generating local oscillator signals (LO), whose I and Q components have a phase difference of 90 ° over the Entire bandwidth, comprising means for generating a Input signal, in particular a signal generator (VCO), a the means for generating the input signal downstream RC-CR filter circuit, which generates a first (S1) and a second (S2) signal, and at least two limiter amplifiers (V1, V2) for amplitude control of the first and the second signal characterized in that - First switching means, in particular CMOS transistors, the first and the second amplitude-controlled Switch signals so that no fundamental wave overlays occur - with help the first switching means generates a first waveform (E1), in which a sine wave follows a cosine wave, and a second waveform (E2) in which a sine wave of an inverted cosine wave follows. Device according to claim 1, in the second switching means, in particular switched capacitance filter or Tact switch, shorten the first (S1) and the second (S2) signal, so in that a first (M1) and a second (M2) modified signal are formed becomes. Device according to claim 2, in which the positive edges of the first (S1) and the second (S2) signals as switching edges for generating the first (M1) and of the second (M2) modified signal. Device according to a the claims 2 or 3, in which a third modified signal (-M2) by inversion of the second modified signal (M2) is generated. Device according to claim 4, wherein the first modified signal (M1) with the third modified signal (-M2), and the first modified signal (M1) with the second modified one Signal (M2) are connected in time. Device according to claim 5, in which the first switching means is adapted to carry out the temporal connection. Apparatus according to any one of the preceding claims, wherein orthogonal harmonic sets are generated for the frequencies f = (2n + 1) · 2 · f ₀ , where f _{0 is} the frequency of a cosine or sine portion and n is an even number. Device according to a of the preceding claims, in which the first (S1) and the second (S2) signal are temporally unsynchronized to each other, wherein the signals are periodic sequences is, and the harmonics of the two signals orthogonal to each other are. Device according to a of the preceding claims, at the higher one Frequency band by multiplying the second signal, in particular a cosine signal, covered with the local oscillator signals becomes. Mobile terminal, in particular mobile device, which is a device according to a of the preceding claims having.