JPS5836018A - Fm receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM receiver G having a search function in which a demodulation circuit and a search stop voltage generation path are improved.

Conventionally, in FM receivers with a search function, when the output of the demodulation circuit has a tuning S curve, the search stop voltage generation circuit generally uses the DC change in the demodulation output to obtain the search stop voltage. However, in this case, there is a problem that due to the temperature characteristics of the counter-tuning stage of the demodulation circuit, if the tuning is shifted, an imbalance occurs in the rise width of the search stop voltage, which leads to a misstop during the search.

Figure 1 shows a conventional FM2 atrature demodulation circuit and its AF
A schematic circuit diagram of a search stop voltage detection circuit using a C (automatic frequency control) output S curve is shown. In the figure,
(1) is the IF input terminal, (2) is the IF amplifier, (4) is the phase coil, (6) is the primary side of the intermediate frequency tuning transformer,
(7) is the secondary side of the tuning transformer, and both include capacitance. (8) is a bypass capacitor, (5)
is a phase comparator that compares the phases of the outputs of the phase coil (4) and the IF amplifier (2), and Ou is the phase comparator (5).
・Audio amplifier, 0η is an audio output terminal, and (9) is an AFC amplifier that outputs a DC voltage according to the difference between the intermediate frequency signal from the phase comparator (5) and the tuned intermediate frequency. Yes, 1 circuit element (4
) to (10) constitute a demodulation circuit that demodulates an intermediate frequency signal and outputs an audio signal. (1 and 14 are operational amplifiers that compare the output voltage of the AFC amplifier (9) with the reference width voltage, +14) (13) are the operational amplifiers + Ill (12+ + half-plane constant resistors that apply their respective reference voltages, ( 15) is an inverter, which includes a search stop voltage generation circuit (support) that generates a stop voltage when the tuning frequency of the demodulation circuit (4) falls within a predetermined frequency range according to the above circuit components (11) to (15). ). (3) is a level detection circuit that detects the level of the F signal of the IF amplifier (2).

Next, the operation will be explained.

The received Ib signal that has passed through the image frequency amplification stage (not shown) and the frequency V number variable stage (not shown) is expressed as an intermediate frequency signal II='
IF large input terminal i (1
), and after being multiplied by the IF amplifier (2),
A phase comparator (5) is added. In addition, the output of the IF amplifier (2) is connected to the phase coil (4) to this phase comparator (5).
), signals with a 90° phase shift are also added by the primary side (6) and secondary side (7) of the tuning transformer, and as a result of the phase comparator (5) acting as a multiplier, the beat component is A demodulated output proportional to the phase difference between the two can be obtained.

This demodulated output is taken out from the audio output terminal (1η) via the audio amplifier (101).The output of the negative phase comparator (5) is sent to the operational amplifier (1) via the AF'C amplifier (9). Here, the output of the AFC amplifier (9) draws an S curve centered around the reference voltage Vs at the tuning center frequency fc, as shown in curve (a) in Figure 3 (therefore, the output of the operational amplifier +111 ( When the bias voltage of 121 is set as Vn and Vr with variable resistors (1, 41+13), fb and fa are above and below the tuning center frequency fc (fa and fb are each circuit constant and adjustment (set equal from this). ), the output of the operational amplifier tllll +12) is turned off, and the search stop voltage output terminal (12) is turned off by the inverter 05).
6) The search stop voltage is obtained. In addition, in the range 1 that is out of tune, the IF from the IF amplifier (2)
The search stop voltage output is turned off by using a mute voltage corresponding to the signal level obtained as a result of applying a portion of the doubled signal to the level detection circuit (3).

Since the above conventional circuit is configured as described above, if the gI&Is curve characteristic deviates as shown in curve (2) in Fig. 4 due to the ambient temperature etc., the frequency f in Fig. 3 above will change.
a, fb become the frequencies fa', fb' shown in FIG. 4, and the balance is lost, resulting in a misstop during the search. In order to prevent this, the tuning transformer size and C temperature coefficient of the demodulation circuit (5) should be selected to the optimum values, or considering the use in areas with narrow receiving channel spacing and the variation in the temperature coefficient of the parts used, A circuit is not necessarily sufficient.

The present invention has been made in view of the problems of the conventional ones as described above, and in order to prevent misstops during searching due to changes in ambient temperature, a part of the tuning capacitance component of the tuning transformer of the demodulation circuit is replaced with a variable capacitance diode. If the tuning S-curve characteristic deviates, the reference voltage at the center of the tuning S-curve characteristic during the search is fed back to the original value, thereby creating a demodulation circuit with a stop voltage rise width that is stable with respect to temperature and a search stop voltage. FM with generation circuit
The purpose is to provide a receiver.

FIG. z2 shows a schematic configuration diagram of an FM radio receiver according to an embodiment of the present invention, and in the figure, the same reference numerals as in FIG. 1 do not indicate the same parts as in FIG. 1. 131 (2) is a resistor that divides the output voltage of the AFC amplifier (9), +211 is the resistance force) (an operational amplifier that amplifies the divided voltage by 241, and 131 (2) is the feedback resistor of the operational amplifier), (19) is ii ]'
Transformation diode 11, (18) is a series capacitor that forms the capacitance component of the secondary side (7) of the tuning transformer together with the variable capacitance diode (19), (20) is a resistor, +26) is a search control unit (not shown) The search mute voltage terminal (2) to which the search mute voltage is supplied is a backflow prevention diode. And "1 circuit elements (211~(
The output of the demodulation circuit is fed back to the variable capacitance diode (1!11) only during the search.

Next, the operation of this circuit will be explained with reference to three parts that are different from the circuit shown in FIG.

Output S curve of AFC amplifier (9) 'City pressure is resistance (2)
岨) The voltage is divided from the bank, and via the operational amplifier ■1),
Series capacitance (181 and demodulation stage tuning transformer 2
A variable capacitance diode (
1! Added to I. Therefore, the deviation due to the temperature of the tuning section becomes a phase difference, which is determined by the deviation of the S-curve characteristic as shown in curve (28) in Figure 4. For example, if this S-curve characteristic is positive in terms of the number of cycles, direction, the DC current 1-11. at the tuning center frequency fc as shown in FIG. The voltage shifts accordingly, and the DC voltage applied to the cathode of the +Ji heavy diode (19) decreases. Therefore, the tuning part te
l is incremented, and as a result, the tuning frequency is pulled back in the negative direction. That is, the +n current level at the tuning center frequency fc becomes the reference voltage Vs, and the balance of the rise width of the stop pressure is also kept constant.

On the other hand, is there a search system for the search mute voltage supply terminal □□□)? A voltage from ll1IQ (not shown) is applied, and it turns off when searching and turns on when receiving, so the variable capacitance diode +1! l) The applied pressure is held in the receiving state.

Note that the description of the two series of operations is only for the case where the S-curve characteristic deviates in the positive direction in terms of frequency, or the circuit of this embodiment similarly performs the correction operation even in the opposite case.

In addition, Fig. 2 shows an example of a quadrature type demodulation circuit, or a ratio detection type demodulation circuit, etc., which has a tuning section with a C configuration and is connected to a demodulation circuit that can obtain an S curve characteristic as a demodulated output. The present invention is applicable to all FM receivers having a stop voltage generating circuit.

As described above, according to the present invention, a part of the tuning capacitance component of the tuning transformer of the demodulation circuit is made into a usable capacitance diode, and when the tuning S-curve characteristic deviates due to a change in ambient temperature, the center of the S-curve characteristic at the time of search is By feeding back the reference voltage back to its original value, it is possible to provide an FM receiver that can obtain a well-balanced stop voltage rise width during a search without being affected by the tuning shift of the demodulation stage due to ambient temperature. There is.

[Brief explanation of the drawing]

Figure 1 shows the quadrature demodulation circuit 2 of a conventional FM receiver.
FIG. 2 is a schematic circuit diagram of an FM receiver according to an embodiment of the present invention, and FIG. 3 shows the output S-curve characteristics in a normal state and the rise and rise of the stop voltage corresponding thereto. FIG. 4 is a diagram showing the S-curve characteristic when the tuning center frequency shifts in the positive direction due to ambient temperature, the rise width of the stop pressure at that time, and the 5-curve characteristic in a state corrected according to the present invention. (2)...Envelope circuit, tl! Jl...variable capacitance diode, (to)...search stop' heavy pressure generation circuit,
Bad... return circuit. The same symbols in the figures indicate the same or equivalent parts. Agent Shin Kuzuno - (9
) 7

Claims (1)

[Claims] (1) In a pM receiver that has a search function that automatically searches for the frequency to be received, it forms a demodulation circuit that demodulates an intermediate frequency signal and outputs an audio signal, and a part of the tuning capacity of this demodulation circuit. a search stop voltage generation circuit that generates a search stop voltage when the tuning frequency of the demodulation circuit is within a predetermined tuning frequency range; 1. An L"M receiver characterized in that it is equipped with a feedback circuit.