JP3861119B2 - Receiver circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a receiver circuit of a communication terminal, and more particularly to a super heterodyne receiver circuit using a filter.
[0002]
[Prior art]
FIG. 8 is a block diagram showing a configuration of a receiving circuit of a conventional super heterodyne communication device terminal. The receiving circuit 200 includes an LNA (low noise amplifier) 10, a mixer (multiplier) 2, a band limiter. SAW filter 3 for quadrature, quadrature detector 4, demodulator 6, and PLL (Phase-Locked Loop) 9.
[0003]
The received signal “Sin (ω0) t” in the carrier frequency band input to the receiving circuit 200 is amplified by the LNA 1 and then input to the mixer 2 that converts the frequency to an intermediate frequency. The mixer 2 mixes the received carrier frequency band received signal “Sin (ω0) t” and the local oscillation signal “Sin (Δω) t” having a predetermined frequency input from the PLL 9 to generate an intermediate frequency ( The IF signal “Sin (ω0 ± Δω) t” is output to the SAW filter 3 after frequency conversion to IF).
This IF signal is band-limited by the SAW filter 3 and then “Sin (ω0−Δω) t”, the I and Q signals are detected by the quadrature detector 4, demodulated by the demodulator 6, and the data and clock Is output as
[0004]
The PLL 9 detects the phase difference between the reference clock from the reference oscillator 13 and the signal from the frequency divider 11 by the PD 12 and outputs a signal corresponding to the phase difference to the VCO 10. A VCO (voltage controlled oscillator) 10 oscillates a signal having a predetermined frequency (local oscillation signal) based on a signal corresponding to the phase difference. The frequency divider 11 divides the signal from the VCO 10 based on a frequency division ratio signal C from a control unit (not shown). As a result, a signal having a predetermined frequency based on the frequency division ratio is output from the PLL 9.
[0005]
In the conventional super-heterodyne receiver circuit, a SAW filter for limiting the band of the intermediate (IF) frequency can be used as much as possible in order to avoid deterioration of reception sensitivity characteristics due to the influence of out-of-band broadband noise and increase in the amount of adjacent channel interference. It is necessary to use one with severe characteristics. Therefore, ideally, a limited band substantially matching the wavelength λ of the input signal 71 of the SAW filter as shown in FIG. 7A is desirable, but in practice, FIGS. ) Is generated (Δωfc ₁ , Δωfc ₂ ), so that the limited bandwidth shown in FIG. 7 (b) is widened in consideration of the variation in the center frequency. A SAW filter having characteristic 72 is used.
[0006]
[Problems to be solved by the invention]
As described above, a super heterodyne communication device using a filter in which the change in the center frequency based on the temperature change is relatively larger than the change in the frequency characteristic (filter characteristic) based on the temperature change as in the conventional SAW filter. In the receiver circuit of the terminal, the band limitation by the filter is less than ideal considering the temperature change, so there is a possibility that the spurious from the mixer, which is a non-linear circuit, may not be sufficiently removed. There has been a problem in that the sensitivity characteristic is deteriorated due to the influence of wideband noise and the amount of adjacent channel interference is increased.
[0007]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a receiving circuit using a filter having a narrower band than the conventional one by compensating for a frequency change due to a temperature change. To do.
[0008]
[Means for Solving the Problems]
FIG. 2 is an explanatory diagram of the frequency change due to the temperature change of the SAW filter. When the input signal 21 has the center frequency ω0 and the wavelength λ as shown in (a), the characteristics of the SAW filter are as shown in (b). Have a width of λ1 to λ2 from the center frequency ω0. Here, as shown in (d), when the band limiting characteristic of the SAW filter becomes a band limiting characteristic 22 ′ shifted in the negative direction by Δ1 due to the temperature change, the input signal 21 shown in (a) becomes the band limiting characteristic 22 ′. When the band limiting characteristic of the SAW filter becomes the band limiting characteristic 22 ″ shifted in the positive direction by Δ2 as shown in FIG. 8F, the input signal 21 is deviated from the band limiting characteristic 22 ′. Since the temperature characteristics of the SAW filter depend on the temperature characteristics of the material and have good reproducibility, it is possible to measure the current temperature and correct the center frequency by associating it with a preset temperature table. In addition, it is known that the electrical characteristics of the SAW filter depend on the size of the electrode on the material, and the characteristic change is small compared to the change of the center frequency. As shown in c) and (e), the input signal 21 is received by shifting the center frequency of the input signal 21 by Δ1 or Δ2 in accordance with the center frequency of the SAW filter that has changed due to the temperature change. A circuit may be configured.
[0009]
The receiving circuit for compensating for this includes a local signal generation circuit, obtains an intermediate frequency from the received wave and the local signal generated corresponding to the received wave, and limits the band of the intermediate frequency by a SAW filter. A receiving circuit that obtains a demodulated signal based on the output is provided with a compensation circuit that generates a compensation signal that compensates for a change in the frequency of the SAW filter based on a temperature change and applies the compensation signal to the local signal generation circuit.
[0010]
The compensation circuit includes a temperature sensor that measures the ambient temperature of the SAW filter, a temperature table in which the temperature and the frequency change value are registered in association with the SAW filter, and a frequency change value that corresponds to the temperature measured by the temperature sensor. And a control voltage converting means for converting to a compensation signal and outputting the compensation signal.
[0011]
The receiving circuit of the necessarily sometimes spectrum frequency control and filter center frequency control does not match. In this case, as shown in FIG. 3, the spectrum 32 is distorted by an amount Δ that deviates from the limited band of the narrow band SAW filter 31 that does not consider the temperature change, and the power is reduced. Therefore, as shown in FIG. 4 (a), by comparing the upper power (FIG. 4 (b)) and the lower power (FIG. 4 (c)) with respect to the spectrum center frequency ω0, the frequency is obtained. It is configured that the filter center frequency is matched with the spectrum center frequency by detecting whether the signal is shifted to the upper side or the lower side and feeding back the detected value (level difference).
[0012]
Specifically, the receiving circuit of the present invention includes a local signal generation circuit, obtains an intermediate frequency from a received wave and a local signal generated corresponding to the received wave, and band-limits the intermediate frequency by a SAW filter. In the receiving circuit for obtaining the demodulated signal based on the output, a control voltage detecting circuit for detecting the level difference between the upper and lower frequencies with reference to the spectrum center frequency based on the output of the SAW filter and supplying it to the local signal generating circuit. It is provided.
[0013]
The control voltage detection circuit includes a first band limiting unit that limits the harmonic component of the upper sideband and a second band limiting unit that limits the harmonic component of the lower sideband separated from the output of the SAW filter. Inverting means for inverting the output of the first band limiting means, phase changing means for changing the phase of the output of the second band limiting means by 90 °, output of the first band limiting means and output of the phase changing means First addition means for adding the output, second addition means for adding the output of the phase conversion means and the output of the inversion means, first level detection means for detecting the output level from the first addition means, The second level detecting means for detecting the output level from the second adding means, and the comparing means for comparing the outputs of the first level detecting means and the second level detecting means to obtain a difference. it can.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing a configuration example of a receiving circuit according to the present invention. A receiving circuit 100 includes an LNA (low noise amplifier) 1, a mixer (multiplier) 2, a band limiting SAW filter 3, and an orthogonal configuration. A detector 4, a control voltage detection circuit 5, a demodulator 6, a compensation circuit 7, an adder 8, and a PLL 9 are provided.
The compensation circuit 7 includes a control voltage conversion circuit 71, a temperature sensor 72, and a temperature table 73, and compensates for a frequency change due to a temperature change of the SAW filter 3 (FIG. 3). In addition, the same part as FIG. 8 attaches | subjects the same code | symbol, and abbreviate | omits description.
[0015]
<First Embodiment>
In FIG. 1, the received wave “Sin (ω0) t” input to the receiving circuit 100 is amplified by the LNA 1 and then input to the mixer 2.
Further, a local oscillation signal (Sin (ΔωL−Δωfc) t) having a predetermined frequency is input from the VCO 10 to the mixer 2.
The mixer 2 mixes the output signal of the LNA 1 (received signal after amplification) and the output signal of the VCO 10 (compensated local frequency signal) and converts them to a predetermined intermediate frequency.
The output signal of the mixer 2 is a SAW filter 3,
ωfc = (ω0−ΔωL) ± Δωfc
Is then converted into an upper sideband (hereinafter referred to as I component) and a lower sideband (hereinafter referred to as Q component) by the quadrature detector 4 and input to the demodulator 6. Here, ΔωL is a local frequency, and Δωfc is a frequency change due to the temperature of the SAW filter 3.
[0016]
[Compensation circuit]
The compensation circuit 7 always measures the temperature of the receiving circuit (especially around the SAW filter 3) with the temperature sensor 72, A / D (analog / digital) converts the measured value, and the temperature and frequency of the SAW filter 3 are previously measured. The relationship (frequency change Δ with respect to temperature change) is made to correspond to the registered temperature table 73, and data for the frequency change corresponding to the measured temperature is extracted and input to the control voltage converter 71, and then D / A (digital / analog) ) A signal that has been converted and compensated for the frequency change due to the temperature change of the SAW filter 3;
Sin (ΔωL ± ωfc) t
Output as.
The output of the compensation circuit 7 is added to the output of the PLL 9 by the adder 8 and fed back to the VCO 10.
With the above configuration, the frequency change of the SAW filter due to a temperature change can be corrected, so that the band limit characteristic of the SAW filter can be set narrower.
[0017]
<Second Embodiment>
In the present embodiment, the center frequency of the SAW filter is matched with the spectrum center frequency, thereby correcting the shift of the center frequency of the SAW filter due to temperature change, and the distortion of the spectrum (shift of the limit band caused by the shift of the center frequency). And prevent power loss.
The present embodiment is an example in which a control voltage detection circuit 5 is provided in the receiving circuit instead of the compensation circuit 7 in FIG. 1. Therefore, there is no input from the compensation circuit 7 to the adder 8. Are supplied with the output of the control voltage detection circuit 5 and the output of the PLL 9.
In FIG. 1, the received wave Sin (ω0) t input to the receiving circuit 100 is amplified by the LNA 1 and then input to the mixer 2.
Furthermore, the local frequency selected by the PLL 9 is input to the mixer 2 so as to be a predetermined intermediate frequency in the VCO 10 with respect to the input frequency.
The reception frequency and local frequency input by the mixer 2 are mixed and converted to a predetermined intermediate frequency.
The output signal of the mixer 2 is band-limited by the SAW filter 3, then converted to an I / Q component by the quadrature detector 4, and input to the control voltage detection circuit 5, and the center frequency is changed (the temperature of the SAW filter is not changed). The I / Q component corrected to ω 0 is output and input to the demodulator 6.
[0018]
[Control voltage detection circuit]
5 and 6 show configuration examples of the control voltage detection circuit.
5 and 6, the control voltage detection circuit 5 includes an LPF (low-pass filter) 51, 51 ′, a Hilbert converter 52, an inverter 53, adders 54, 54 ′, and an HPL (high-pass filter). ) 55 and 55 ′, level detectors 56 and 56 ′, and a comparison circuit 57.
[0019]
In FIG. 5, the harmonic component of the I component signal Sin ((ω0−ΔωL) ± Δωfc) t · Sin (ω0) t output from the quadrature detector 4 is band-limited by the LPF 51 of the I term. At the output end of the LPF 51, when the frequency is shifted higher by + Δfc than the desired frequency, the signal component of + (1/2) · CosΔωt is − (1/2) when the frequency is shifted by −Δfc lower than the desired frequency. -The signal component of CosΔωt remains.
Next, in the term I, the output of the LPF 51 (the remaining signal component) is input to the adder 54, and the sign is inverted by an inverting circuit (for example, an operational amplifier) 53 and input to the adder 54 ′.
On the other hand, the Q component signal Sin ((ω0−ΔωL) ± Δωfc) t · Cos (ω0) t ′ output from the quadrature detector 4 is band-limited by the LPF 51 ′ of the Q term. At the output end of the LPF 51 ′, when the frequency is shifted higher by + Δfc than the desired frequency, the signal component of + (1/2) · SinΔωt is − (1/2) when the frequency is shifted by −Δfc lower than the desired frequency. ). The signal component of SinΔωt remains.
[0020]
Next, in the Q term, by changing the phase by 90 degrees by the Hilbert transformer 52, the signal of ± (1/2) · SinΔωt is converted into the signal of ± (1/2) · Cosωt, and the adder 54 ′ and the addition Input to the device 55. The output of the adder 55 of the I term is removed by the HPF 55 to emphasize the spectral distortion, the level is detected by the level detector 56, input to the demodulator 6 as the I component, and compared with the comparison circuit 57. Is input. Further, the output of the Q term adder 55 'is also subjected to removal of a low frequency component by the HPF 55 in order to emphasize the distortion of the spectrum, detected by the level detector 56', and input to the demodulator 6 as a Q component. , Input to the comparison circuit 57. In the comparison circuit 57, after comparing the levels, the difference vc is input to the adder 8 as a control voltage and fed back to the VCO 10, whereby the error of the center frequency can be reduced and the distortion of the spectrum can be reduced. In the present embodiment, the Hilbert converter 52 is provided on the Q term side, but may be provided on the I term side as shown in FIG. In this case, the output signal (I term) of the Hilbert transformer 52 becomes ho be off-center frequency in either up or down pot (1/2) · ΔSinωt.
[0021]
<Third Embodiment>
This embodiment is an example in which both the control voltage detection circuit 5 and the compensation circuit 7 are provided as shown in FIG. 1, that is, an example in which the above-described first and second embodiments are combined. Therefore, the output of the orthogonal transformer 4 is input to the control voltage detection circuit 5, and the I component and Q component of the output of the control voltage detection circuit 5 are input to the demodulator 6, and the control voltage is input to the adder 8. Further, the compensation signal from the compensation circuit 7 (a signal (control voltage) in which the frequency change due to the temperature change of the SAW filter 3 is compensated) is input to the device 8.
[0022]
In this way, by combining the first and second embodiments, the signal circuit 100 is configured as a receiving circuit that is resistant to signal interference.
The received wave Sin (ω0) t input to the receiving circuit 100 in FIG. 1 is amplified by the LNA 1 and then input to the mixer 2.
Further, the mixer 2 has a control voltage (a sum of the VCO characteristic from the control voltage detection circuit 5 and the compensation signal from the compensation circuit 7) in consideration of the temperature change and spectrum distortion of the SAW filter 3 with respect to the input frequency. A local signal Sin (ΔωL ± Δωfc) t controlled to have a predetermined intermediate frequency is input by the VCO 10 using.
The mixer 2 mixes the output signal of the LNA 1 (the amplified received signal) and the output signal of the VCO 10 and converts them to a predetermined intermediate frequency.
[0023]
The output signal of the mixer 2 is a band-limited signal Sin ((ω0−ΔωL) ± Δωfc) t by the SAW filter 3, and is divided into an I component and a Q component by the quadrature detector 4, and the control voltage detection circuit 5 Spectral distortion is detected, and the detection result is input to the adder 8 as a control voltage having VCO characteristics. The adder 8 is supplied with a control voltage taking into account the temperature change of the SAW filter 3 from the compensation circuit 7. The sum of these control voltages is fed back to the VCO 10.
As a result, the temperature change of the SAW filter 3 can be compensated, and the error of the center frequency can be reduced, so that a stable signal characteristic can be obtained, the receiving sensitivity is good, and a receiving circuit resistant to adjacent channel interference can be configured.
Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made.
[0025]
【The invention's effect】
As described above , according to the present invention , the control voltage from the control voltage detection circuit is fed back to the VCO, and the filter center frequency is matched with the spectral frequency control, so that the shift of the center frequency of the SAW filter due to temperature change is achieved. Therefore, it is possible to prevent spectral distortion (shift in the limit band caused by shift in the center frequency) and power reduction.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration example of a receiving circuit according to the present invention.
FIG. 2 is an explanatory diagram of a frequency change due to a temperature change of the SAW filter.
FIG. 3 is an explanatory diagram of distortion of a spectrum center frequency.
FIG. 4 is an explanatory diagram of distortion detection at a spectrum center frequency.
FIG. 5 is a diagram illustrating a configuration example of a control voltage detection circuit.
FIG. 6 is a diagram illustrating a configuration example of a control voltage detection circuit.
FIG. 7 is an explanatory diagram of a frequency change due to a temperature change of the SAW filter.
FIG. 8 is a block diagram showing a configuration of a conventional receiving circuit.
[Explanation of symbols]
3 SAW filter 5 Control voltage detection circuit 7 Compensation circuit 8 Adder (local signal generation circuit)
9 PLL (Local signal generator)
10 VCO (voltage controlled oscillator; local signal generation circuit)
51, 51 ′ LPF (low-pass filter; first and second band limiting means)
52 Hilbert converter (phase conversion means)
53 Inversion circuit (inversion means)
56, 56 'level detector (level detection means)
57 Comparator (comparison means)
71 Control voltage conversion circuit (compensation circuit)
72 Temperature sensor (compensation circuit)
73 Temperature table (compensation circuit)
100,200 receiving circuit

Claims (1)

A local signal generation circuit is provided, and an intermediate frequency is obtained by mixing the received wave and the local signal generated in the received wave, the intermediate frequency is band-limited by a SAW filter, and a demodulated signal is obtained based on the output. In the receiving circuit,
A control voltage detection circuit that detects a difference in level between the upper and lower frequencies with reference to the spectrum center frequency based on the output of the SAW filter, and supplies the level difference to the local signal generation circuit ;
The control voltage detection circuit separates the output of the SAW filter from the first band limiting means for limiting the harmonic component of the upper sideband and the second band limiting means for limiting the harmonic component of the lower sideband. When,
Inverting means for inverting the output of the first band limiting means;
Phase shifting means for phase shifting the output of the second band limiting means by 90 °;
First addition means for adding the output of the first band limiting means and the output of the phase shift means;
Second addition means for adding the output of the phase conversion means and the output of the inversion means;
First level detecting means for detecting an output level from the first adding means;
Second level detection means for detecting an output level from the second addition means;
Comparison means for comparing the outputs of the first level detection means and the second level detection means to obtain a difference;
Reception circuit characterized in that it comprises a.

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