JPH1013191A - Automatic frequency control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the automatic frequency control circuit with a simple configuration which does not malfunction, even when a center frequency of a filter applying band limit to an intermediate frequency deviates in a receiver for mobile communication. SOLUTION: A signal from an antenna 1 is amplified by an RF amplifier 3 through a switch 2, a mixer 4 mixes the RF input and a signal LO1 given to a terminal LO, to convert the signal frequency into an intermediate frequency IF 1. The filter 5 eliminates an excess harmonic component or the like from the IF 1, and the mixer 6 mixers the RF input and a signal LO2 given to a terminal LO, to convert the signal frequency into an intermediate frequency signal IF 2. A filter 7 applies band limit to the IF 2, and an LMT amplifier r applies amplitude limit to the IF 2 and the result is sent to a demodulation section. A counter 9 counts the number of pulses from an output signal of an LMT amplifier 8. The count of the counter 9 is compared with a reference value which has been preset in a decision circuit 10, and the decision circuit 10 outputs a frequency revision data signal to a local oscillator 12 in the case of non-coincidence.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic frequency control circuit, and more particularly to an automatic frequency control circuit for making a quadrature modulation signal input from an antenna of a quadrature demodulation type receiver follow a regular intermediate frequency.

[0002]

2. Description of the Related Art As a first example of this kind of conventional technology,
"Frequency discrimination circuit" described in JP-A-62-30411 can be mentioned.

The first conventional frequency discriminating circuit comprises a detection voltage obtained by passing an intermediate frequency through a band limiting filter centered on a frequency higher than a predetermined intermediate frequency f0, and a frequency lower than the intermediate frequency. The local oscillation frequency is controlled by detecting a frequency shift of the intermediate frequency signal based on a comparison value with a detection voltage obtained by passing the intermediate frequency signal through a band-limiting filter having a center at the center.

As a second conventional example, Japanese Utility Model Application Laid-Open No.
The “tuner for receiving satellite broadcasting” described in JP-A-6133 can be mentioned.

[0005] The satellite broadcast receiving tuner of the second conventional example has a configuration in which an intermediate frequency is counted by a reference clock and a local oscillation frequency is controlled so as to be a count value corresponding to a normal intermediate frequency. I have.

[0006]

In this first conventional example, a filter having a center frequency higher than the intermediate frequency and a filter having a center frequency lower than the intermediate frequency are provided in addition to the filter that passes the original intermediate frequency. However, since these filters need a parameter adjustment circuit and a detection circuit for each of these filters, the circuit scale becomes large and it is not economical.

Further, in the second conventional example, a signal input at a normal intermediate frequency is cut off a part of the input modulated signal spectrum due to a shift of the center frequency of the filter. The counter does not reach the count value corresponding to the above, and the counter judges this value as the frequency deviation of the input signal and changes the frequency of the local oscillator, resulting in malfunction of the automatic frequency control circuit. Was. That is, when the center frequency of the filter used for limiting the intermediate frequency signal band is shifted after the conversion to the intermediate frequency, the automatic frequency control circuit malfunctions.

Accordingly, an object of the present invention is to provide a receiver for mobile communication which does not malfunction even if the center frequency of a filter for band-limiting an intermediate frequency is shifted.
An object of the present invention is to provide an automatic frequency control circuit having a simple configuration.

[0009]

According to the present invention, a first mixer for generating a first intermediate frequency signal by multiplying a quadrature modulated signal input from an antenna by an output signal of a first local oscillator. A first filter for removing extra harmonic components from the first intermediate frequency signal; and a second intermediate frequency by multiplying the first intermediate frequency signal by an output signal of a second local oscillator. A second mixer for generating a signal;
In a mobile communication receiver comprising a second filter for limiting a band of the second intermediate frequency signal and a limiter amplifier for limiting an amplitude of an output signal of the second filter, an output pulse of the limiter amplifier is provided. And a determination circuit for determining whether to turn on or off the switch based on the count value of the counter, and a determination circuit provided between the antenna and a radio frequency terminal of the first mixer. An automatic frequency control circuit comprising: the switch that enables the quadrature modulation signal to be disconnected for an arbitrary time by a switching signal.

Further, there is provided an automatic frequency control circuit characterized in that the counter counts output pulses of the limiter amplifier for a predetermined time and outputs the count value.

Further, there is provided an automatic frequency control circuit characterized in that the second local oscillator varies its transmission frequency in accordance with a frequency change data signal from the determination circuit.

Further, the determination circuit outputs the switching signal to turn off the switch for an arbitrary time, and when the switch is off, the count value input from the counter is the center value of the second intermediate frequency signal. When the frequency is equal to a value obtained by multiplying the time during which the counter is counting the output pulse of the limiter amplifier, this value is set as a reference value, whereby an automatic frequency control circuit is obtained.

[0013] Then, the determination circuit determines that the count value input from the counter when the switch is in the off state is the time when the counter is counting the output pulse of the limiter amplifier at the center frequency of the second intermediate frequency. When the value is not equal to the multiplied value, an automatic frequency control circuit characterized by setting a value obtained by multiplying this value by a correction coefficient as a reference value is obtained.

The determination circuit compares the count value input from the counter with the reference value when the switch is on, and when the count value does not match the second count value, the second value is set to the second value.
An automatic frequency control circuit for outputting frequency change data for adjusting the frequency of the local oscillator.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the operation of the present invention will be described. A quadrature modulated signal input from an antenna is converted into a second intermediate frequency through two mixers, and band-limited by a filter.

If the center frequency of the filter deviates from the center frequency of the second intermediate frequency, the decision circuit turns off the switch once before the receiver enters the operation state.

At this time, the thermal noise and the noise frequency of the receiver are amplified, band-limited by a filter, passed through a limiter, and the number of noise pulses is counted by a counter.

Here, if the filter has a shift in the center frequency, the counter counts a value different from the count value when there is no shift in the center frequency. The determination circuit sets a reference value based on the value at this time.

Next, the switch is turned on by a signal from the determination circuit, and the receiver enters a normal operation state.

Even when a signal having no deviation in the center frequency comes from the antenna, the value counted by the counter due to the deviation of the center frequency of the filter becomes a value different from the theoretical value (the reference value set previously).

However, since the judgment circuit has this value as a reference value and they match, the judgment circuit does not send the frequency change data signal to the local signal oscillator. Therefore, in the automatic frequency control circuit of the present invention,
Malfunction can be avoided.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the automatic frequency control circuit of the present invention.

Referring to FIG. 1, an automatic frequency control circuit in a mobile communication receiver according to this embodiment includes an antenna 1
A first mixer 4 for multiplying a quadrature modulated signal inputted from the RF amplifier (RF amplifier) 3 and amplified by a radio frequency amplifier (RF amplifier) 3 with an output signal LO1 of a first local oscillator 11 to generate a first intermediate frequency signal IF1 And a first intermediate frequency signal IF1
Multiplying the first intermediate frequency signal IF1 of the output of the first mixer 4 and the output signal LO2 of the second local oscillator 12 by the first filter 5 which performs the band limitation of the first filter 5 To generate the second intermediate frequency signal IF2
Mixer 6, a second filter 7 for limiting the band of the second intermediate frequency signal IF2, and a limiter amplifier (LMT amplifier) 8 for limiting the amplitude of the output signal of the second filter 7.
, A counter 9 for counting output pulses of the LMT amplifier 8, and a switch 2 based on the count value of the counter 9.
And a decision circuit 10 provided between the antenna 1 and the RF amplifier 3.
And a switch 2 for disconnecting the quadrature modulation signal for an arbitrary time by a switching signal from 0.

The signal input from the antenna 1 is input to the RF amplifier 3 when the switch 2 is turned on (shown by a broken line), but is output when the switch 2 is turned off (shown by a solid line).
Not input to amplifier 3.

When the signal input to the RF amplifier 3 through the switch 2 and amplified by the RF amplifier 3 is input to the radio frequency terminal RF of the mixer 4, the mixer 4 is input to the RF input and the local signal frequency terminal LO. Local oscillator 11
With the first output signal LO1 to convert it into a first intermediate frequency signal IF1.

When the first intermediate frequency signal IF1 is input to the radio frequency terminal RF of the mixer 6 after excess harmonic components and the like are removed by the filter 5, the mixer 6 receives the RF input and the local signal frequency. The output signal LO2 of the local oscillator 12 input to the terminal LO is mixed with the second
To the intermediate frequency signal IF2.

The second intermediate frequency signal IF2 is band-limited by the filter 7 and amplitude-limited by the LMT amplifier 8, and then transmitted to the demodulation unit.

The output signal of the LMT amplifier 8 is supplied to a counter 9, and the counter 9 counts the number of pulses of the output signal of the LMT amplifier 8. Then, this count value is compared with a reference value preset in the determination circuit 10, and the determination circuit 10 outputs a frequency change data signal to the local oscillator 12 only when the values do not match.

Here, the influence of the malfunction of the automatic frequency control circuit due to the center frequency shift of the intermediate frequency filter when the receiver for receiving the quadrature modulated signal is synchronized by the synchronous detection method will be described.

In the case of the synchronous detection method, the frequency of the input signal must exactly match the clock frequency for achieving bit synchronization. For example, if the clock frequency for achieving bit synchronization is 450 kHz, the second intermediate frequency must also be correctly 450 kHz.

When the automatic frequency control circuit malfunctions due to the center frequency shift of the intermediate frequency filter, and the second intermediate frequency becomes 451 kHz, for example, the phase tracking lock is released and a burst error occurs.

On the other hand, when the receiver for receiving the quadrature modulated signal is synchronized by the delay detection method, no loss of synchronization occurs, but a slight bit error rate (BER) occurs. ) Is inevitable.

Next, the operation of this embodiment will be described with reference to FIGS.

FIG. 2 is a waveform diagram when the center frequency is not shifted in the second filter in the switch-off state in FIG. 1, and FIG. 3 is a frequency shift in the switch-on state in FIG. 1 and the second filter. FIG. 4 is a waveform diagram when a signal without a frequency shift is input when there is no signal, and FIG. 4 is a diagram when a signal with a shift in center frequency is input to the second filter in the switch-on state in FIG. FIG. 5 is a second waveform diagram having a shift in the center frequency in FIG.
FIG. 6 is a waveform diagram for explaining the operation of the filter shown in FIG.
In the switch-on state in the above, when a signal having a shift in the center frequency is input, the second signal having a shift in the center frequency
FIG. 6 is a waveform diagram for explaining the operation of the filter of FIG.

First, the operation of the automatic frequency control circuit when the switch 2 is turned off is shown in FIGS.
This will be described with reference to FIG.

FIG. 2A shows the waveform of the filter 7 in FIG. 1 and f0 is the center frequency of the second intermediate frequency signal IF2. FIG. 2B shows the noise spectrum after passing through the filter 7, and the difference in the center frequency of the waveform after passing through the filter 7 appears as the difference in the count value of the counter 9.

FIG. 5A shows the waveform of the filter 7 when the switch 2 in FIG. 1 is in the "OFF" state.

The decision circuit 10 sends a switch signal to the switch 2 so as to turn off the input signal from the antenna 1. Therefore, since there is no input to the RF amplifier 3, the RF
Thermal noise (represented by kTBF) is amplified and appears at the output of the amplifier 3.

The amplified kTBF is input to the radio frequency terminal RF of the mixer 4, and the noise converted into the first intermediate frequency signal IF 1 by the mixer 4 passes through the filter 5 and is input to the radio frequency terminal RF of the mixer 6. And mixer 6
Is further converted into a second intermediate frequency signal IF2.

The second intermediate frequency signal IF2 (frequency =
The noise converted to f) is band-limited by the filter 7 to have a waveform shown in FIG. 2B, and is band-limited by the LMT amplifier 8.

The counter 9 counts the number of output pulses of the LMT amplifier 8 for a certain period of time (= T1) and sends it to the determination circuit 10. Then, the determination circuit 10 determines and stores a reference value based on the count value (C1) at this time.

At this time, if there is no deviation in the center frequency of the filter 7, the ideal count value C1 = 2 shown in FIG.
f0 × T1 is obtained. The determination circuit 10 uses this ideal count value C1 as a reference value.

If there is a shift Δf in the center frequency f0 of the filter 7, the waveform shown in FIG. 5A is obtained, and the count value C1 ′ = (f + Δf) T1 is obtained. This count value C1 'is different from the ideal count value C1.
At this time, a value obtained by multiplying the count value C1 'by the correction coefficient α is used as a reference value. (Here, α is a correction coefficient (0) that is multiplied only when the reference value deviates from the ideal reference value f0 × T1.
In 1), the optimum value is obtained in advance by experiment or the like).

Next, the operation of the automatic frequency control circuit when the switch 2 is turned on will be described with reference to FIGS.

FIG. 3A shows the waveform of the filter 7 in FIG. 1 and the input signal to the filter 7, and f0 is the center frequency of the second intermediate frequency signal IF2. Also,
FIG. 3B shows a signal waveform after passing through the filter 7, and f0
Is the center frequency of the signal input to the counter 9.

FIGS. 4A and 4C show filters 7
4 shows a waveform of an input signal to the filter 7 and FIG.
(B) and (d) show the waveform of the signal after passing through the filter 7.

When the decision circuit 10 sends a switch signal to the switch 2 so as to bring the input signal from the antenna 1 into “contact”, the signal input to the RF amplifier 3 is amplified by the RF amplifier 3.

The amplified signal is input to the radio frequency terminal RF of the mixer 4, and the signal converted into the first intermediate frequency signal IF 1 by the mixer 4 passes through the filter 5 and is input to the radio frequency terminal RF of the mixer 6. The signal is further converted by the mixer 6 into a second intermediate frequency signal IF2.

The second intermediate frequency signal IF2 (frequency =
The signal converted to f) is band-limited by the filter 7, and
The amplitude is limited by the LMT amplifier 8.

The counter 9 counts the number of pulses output from the LMT amplifier 8 for a certain period of time (= T1) and sends it to the determination circuit 10. Then, the determination circuit 10 compares the count value (= C2) at this time with a reference value.

At this time, as shown in FIG. 3B, if the count value C2 = f0 × T1, the determination circuit 10 determines that there is no deviation in the frequency of the signal input from the antenna 1, and The transmission of the frequency change data is not performed.

As shown in FIGS. 4A and 4B,
If the reference value> count value C2, the determination circuit 10 determines that the center frequency f1 of the input signal from the antenna 1 is shifted to a lower side than the center frequency f0 of the filter 7, and the local oscillators 11 and 12 are both lower.・ When local
The frequency change data is transmitted to the local oscillator 12 so as to lower the frequency.

If the reference value is smaller than the count value C2 as shown in FIGS. 4C and 4D, the judgment circuit 10
Determines that the center frequency f2 of the input signal from the antenna 1 is higher than the center frequency f0 of the filter 7, and when the local oscillators 11 and 12 are both lower local, Is transmitted so as to increase the frequency.

Next, the center frequency of the filter 7 is shifted (=
The operation when Δf) exists will be described with reference to FIGS.

FIG. 5B shows the filter 7 when a signal of a normal frequency is input to the filter 7 having a center frequency shift in the switch-on state, and the waveform of the input signal to the filter 7. (C) shows the waveform after passing through the filter 7 in FIG.

In FIG. 5C, the count value C2 =
(F0 + Δf ′) T1. Conventionally, since f0 × T1 is used as the reference value, the automatic frequency control circuit operates to move the input signal further to the left. However, in the present embodiment, the reference value = (f0 + Δf) T1 × α = (f0 + Δf ′) T1. There is no misoperation.

FIGS. 6A and 6C show the filter 7 and the waveform of the input signal to the filter 7, and FIG.
(B) and (d) show the waveforms after passing through the filter 7 in FIGS.

In FIG. 6A, reference value = (f0 + Δ
f) T1 × α, and the count value C in FIG.
Since 2 = (f0 + Δf) T1 and the count value> the reference value, the automatic frequency control circuit normally operates so that the input signal moves to the left, and moves until the waveform shown in FIG.

In FIGS. 6C and 6D, the count value C
Since 2 = f0 × T1 and the count value <the reference value, the automatic frequency control circuit operates so that the input signal moves rightward.

That is, it is expected that the count value will not be C1 due to the influence of the center frequency shift of the filter 7 even if there is no frequency shift in the input signal from the antenna 1, but in the determination circuit 10 of this embodiment, 7, the value multiplied by the correction coefficient α in consideration of the deviation Δf of the center frequency is used as the reference value, so that it is determined that there is no frequency deviation in the input signal from the antenna 1 and the local oscillator 12 Is not sent.

It should be noted that B.I. of the receiver due to the influence of the steep operation of the automatic frequency control circuit. E. FIG. In order to prevent the deterioration of R, the frequency of the local oscillator 12 is corrected several times.
That is, instead of making a large correction at once, the amount of one correction is determined in advance in consideration of the transmission rate, the intermediate frequency, and the like, and the data sent from the counter 9 is determined by the determination circuit 10. The cycle in which the frequency of the local oscillator 12 is changed is executed several times so as to end the cycle.

In the present embodiment, the decision circuit 10 does not send a frequency change data signal to the local oscillator 12 such that the count value C2 is set to the reference value at one time. The frequency correction amount of the local oscillator 12 is selected so as to be controlled to the reference value.

As a result, the count value C 2 gradually approaches the reference value, becomes equal at the eleventh time, and the transmission of the frequency change data signal to the local oscillator 12 is stopped.

In this way, the B.I. of the receiver is affected by the steep operation of the automatic frequency control circuit. E. FIG. The deterioration of R can be prevented.

In this embodiment, the reference value of the determination circuit 10 is set in advance. However, the reference value is reset as needed, for example, when the receiver is started or several times a year. You may do it.

[0066]

As described above, the present invention provides a first mixer for generating a first intermediate frequency signal by multiplying a quadrature modulated signal input from an antenna by an output signal of a first local oscillator. Generating a second intermediate frequency signal by multiplying the first intermediate frequency signal by an output signal of a second local oscillator and a first filter for removing an extra harmonic component from the first intermediate frequency signal In a mobile communication receiver comprising: a second mixer for performing the above operation, a second filter for performing a band limitation of the second intermediate frequency signal, and a limiter amplifier for performing an amplitude limitation of an output signal of the second filter. A counter that counts output pulses of the limiter amplifier, a determination circuit that determines whether to turn the switch on or off based on the count value of the counter, and a circuit between the antenna and the radio frequency terminal of the first mixer. A switch for enabling the quadrature modulation signal to be cut off for an arbitrary time by a switching signal from the kettle determination circuit, and the counter counts output pulses of the limiter amplifier for a predetermined time and outputs the count value. Further, the second local oscillator varies its transmission frequency by the frequency change data signal from the determination circuit, and further, the determination circuit outputs a switching signal to turn off the switch for an arbitrary time. When the count value input from the counter in the off state of the switch is equal to the value obtained by multiplying the center frequency of the second intermediate frequency signal by the time during which the counter is counting the output pulses of the limiter amplifier, this value is used as a reference value. By setting, the judgment circuit inputs from the counter when the switch is in the off state. If the counted value is not equal to the value obtained by multiplying the center frequency of the second intermediate frequency by the time during which the counter is counting the output pulses of the limiter amplifier, a value obtained by multiplying this value by a correction coefficient is set as a reference value. And the determination circuit compares the count value input from the counter with the reference value when the switch is on, and outputs frequency change data for adjusting the frequency of the second local oscillator when they do not match. This eliminates the need for a filter having a center frequency higher than the intermediate frequency and a filter having a center frequency lower than the intermediate frequency, and further eliminates the need for a parameter adjustment circuit and a detection circuit required for each of these filters. This has the effect of contributing to downsizing and realizing economy.

Also, by setting the reference value by counting the number of noise pulses when the signal from the antenna is turned off by a switch in advance, the reference value is set in consideration of the center frequency shift of the filter. Therefore, it is possible to prevent the automatic frequency control circuit from malfunctioning due to deviation of the center frequency of the filter due to individual variation or aging.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an automatic frequency control circuit of the present invention.

FIG. 2 is a waveform diagram in a switch-off state in FIG. 1 and when there is no shift in center frequency in a second filter.

FIG. 3 is a waveform diagram when a signal without a frequency shift is input in a switch-on state in FIG. 1 and when there is no frequency shift in a second filter.

FIG. 4 is a waveform diagram when a signal having a shifted center frequency is input to a second filter in the switch-on state in FIG. 1 and having no shift in the center frequency.

FIG. 5 is a waveform chart for explaining an operation of a second filter having a shift in center frequency in FIG. 1;

FIG. 6 is a waveform diagram for explaining the operation of a second filter having a shift in center frequency when a signal having a shift in center frequency is input in a switch-on state in FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 antenna 2 switch 3 radio frequency amplifier (RF amplifier) 4, 6 mixer 5, 7 filter 8 limiter amplifier (LMT amplifier) 9 counter 10 decision circuit 11, 12 local oscillator IF1, IF2 intermediate frequency signal LO local signal frequency terminal LO1, LO2 Output signals of local oscillators 11 and 12 RF radio frequency terminal

Claims (6)

[Claims] A first mixer for multiplying a quadrature modulated signal input from an antenna by an output signal of a first local oscillator to generate a first intermediate frequency signal; A first filter for removing extra harmonic components, a second mixer for multiplying the first intermediate frequency signal by an output signal of a second local oscillator to generate a second intermediate frequency signal, In a mobile communication receiver comprising a second filter for limiting a band of the second intermediate frequency signal and a limiter amplifier for limiting an amplitude of an output signal of the second filter, an output pulse of the limiter amplifier is provided. A counter for counting the number of switches, a determination circuit for determining whether to switch on or off based on the count value of the counter, and a radio frequency terminal of the first mixer provided between the antenna and the first mixer. An automatic frequency control circuit comprising: a switch for enabling the quadrature modulation signal to be cut off for an arbitrary time by a switching signal from the determination circuit. 2. The automatic frequency control circuit according to claim 1, wherein said counter counts output pulses of said limiter amplifier for a predetermined time and outputs the count value. 3. The automatic frequency control circuit according to claim 1, wherein said second local oscillator changes its oscillation frequency in response to a frequency change data signal from said determination circuit. 4. The determination circuit outputs the switching signal to turn off the switch for an arbitrary time, and when the switch is off, a count value input from the counter is a center frequency of the second intermediate frequency signal. 2. The automatic frequency control circuit according to claim 1, wherein when the counter is equal to a value obtained by multiplying a time for counting the output pulses of the limiter amplifier, this value is set as a reference value. 5. The determination circuit according to claim 1, wherein the count value input from the counter in the off state of the switch is set to the center frequency of the second intermediate frequency, and the time during which the counter counts the output pulse of the limiter amplifier is determined. 2. The automatic frequency control circuit according to claim 1, wherein when the value is not equal to the multiplied value, a value obtained by multiplying the value by a correction coefficient is set as a reference value. 6. The frequency change data for adjusting the frequency of the second local oscillator when the count value input from the counter is not equal to the reference value while the switch is in an on state. 4. The automatic frequency control circuit according to claim 1, wherein