JPS615630A - FM receiver - Google Patents

Abstract

PURPOSE:To decrease the number of capacitors which transmit a detection output by obtaining a either of S-curve detection outputs of the FM detection output by using the FM detection output and a reference voltage which are antiphase with each other. CONSTITUTION:When a switch SW is connected to a contact (a) and a current shown by an arrow is in the audio frequency band, current variation at a point A is grounded and an output signal V0 responding to an audio signal is obtained from an operational amplifier A1. Simultaneously, a voltage developed at one terminal of a capacitor CA is supplied as an AFC signal to a local oscillation circuit 14. When the switch SW is switched to a contact (b), on the other hand, an output signal V0 which has the same amplitude and is antiphase with the signal at the point A appears at an output terminal Z, and the voltage developed at one terminal of the capacitor CA is supplied as the AFC signal to the local oscillation circuit 14. The output signal V0 from a terminal 7 is supplied to an FM demodulating circuit through a coupling capacity to obtain an R and an L signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an FM receiver, and particularly to a technique that is effective when supplying FM detection output to a stereo demodulation circuit.

[Background technology]

FIG. 1 is a circuit diagram showing the relationship between an FM detector 1 and a stereo demodulation circuit 2, which were investigated by the inventors prior to the invention of the present application. From the FM detector 1, a detection output known as a so-called figure-eight curve is obtained, and this detection output is described in the ``FM Tools Manual'' (1st edition reprinted on September 1, 1978, ■It is described in detail in Radio Gijutsusha, written by Akira Kuroyo.

Since the above FM detection output has an S curve, for example, the FM frequency is high due to the detuned state, etc.
In the case where the voltage remains at the S curve shown in the figure, the DC voltage appears to be at a high level. Therefore, the FM detection output cannot be directly supplied to the demodulation circuit 2 at the next stage, and a capacitor is required to cut off the DC component.

By the way, when the power supply voltage of the FM detector 1 and the power supply voltage of the demodulation circuit 2 are relatively low voltages and have close voltage levels, the bias voltage of the demodulation circuit 2 is initially limited to a specific range. . If you try to connect the output terminal of the FM detector l and the input terminal of the demodulation circuit 2 with one capacitor, the voltage swing of the detection output will change depending on the polarity of the connection, in other words, from negative voltage to positive voltage. The voltage level up to is limited. In this case, high output cannot be obtained, so two electrolytic capacitors C, ,C with polarity as shown in Fig.
, is connected so that problems such as destruction of capacitors c, , 'c1 will not occur no matter what level of positive voltage the detection output is, and the input bias voltage of the demodulation circuit can be set to any level of positive voltage. I am trying to get it to work without any problems.

However, such a circuit configuration requires two electrolytic capacitors with a large capacity and a large amount of dust. Therefore, when an FM receiver or the like is fabricated into a semiconductor integrated circuit, the electrolytic capacitors must be externally attached as components. As a result, the inventors have investigated the problem of increasing the number of external connection terminals, increasing production costs, and lowering the packaging density.
revealed.

[Object of the invention,]

The present invention was made in view of the above-mentioned circumstances, and its purpose is to reduce the number of DC blocking capacitors provided between an FM detector and a stereo demodulation circuit to transmit the detected output. The object of the present invention is to provide an FM receiver that can obtain the desired results.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief summary of the invention disclosed in this application is as follows:
This is 9 below.

In other words, F is supplied to points A and B with opposite phases to each other.
One of the AC components of the M detection output is removed by switch SW and capacitor C, and the DC component and the other AC component are transmitted and added, and then supplied to the amplifier circuit AI, which is then sent to the subsequent FM demodulation circuit. is added to the desired bias voltage of the amplifier circuit A1, which is set in relation to the bias voltage of f.
By superimposing the cFM detection output, the FM detector and F
This reduces the coupling capacitor between the M demodulation circuit and the M demodulation circuit.
This achieves the objectives of the invention.
' [Example-1] Next, the first example of the FM receiver to which the present invention is applied will be described as a second example.
This will be explained with reference to the figures and FIG.

Figure 2 shows the F from the receiving antenna of an IC-based FM receiver.
It shows the circuit configuration up to the M detector, and the circles surrounding the numbers are external connection terminals. In the above FM receiver, the present invention is shown as a circuit block after the FM detector, and the above circuit block is interposed between the FM detector and the stereo demodulation circuit shown in FIG. Become. Therefore, in the explanation of the embodiment, for convenience of explanation, the explanation will be given sequentially starting from the antenna input.

Antenna 11. High frequency amplifier circuit 122 frequency mixed circuit 1
31 local oscillation circuit 140 circuit configuration and circuit operation are as follows:
It is well known among those skilled in the art. The above mixing circuit 13
The output signal is introduced into the ICM via the coupling capacitor CSt, and is amplified and amplitude-limited by the FMIPIJ transmitter, which is configured by multistage-connected differential amplifiers DA1 to DA1, and is amplitude-limited to eliminate undesired AM. components are removed.

On the other hand, a predetermined DC NF is connected from the output of the differential amplifier DAI to the differential amplifier Dm1 by a capacitor 01h and a resistor R11.
B is applied to stabilize the bias of the differential amplifiers DAs to Dm. Also, the differential amplifiers DAi and D
A ceramic filter 15 having a predetermined pass band is connected between the two.

Thus, two mutually opposite phase output signals obtained from the differential amplifier Dm as a buffer amplifier are supplied to each base of the transistor Qs = Q* to operate as a buffer amplifier. The output voltage of the transistors Qs, Q* is the emitter resistor R3,.

It is obtained as a voltage drop of Ro, and is supplied to the double-balanced differential amplifier circuit 31 at the next stage. And transistor Q, ~
A phase shifter 30 (for example, phase shifted by 90° at a center frequency of 10.7 MHz) and 4 constituted by the double balanced differential amplifier 31 consisting of Qs and a coil LSI capacitor C11+C@@rC14. , constitutes a well-known quadrate air detector, and generates S biopsy wave outputs S, , S, with opposite phases to each other at nodes N,,N,. Hikoo,
The reference voltage VIICFI determines the bias voltage of the transistors Q1 to Qi via the resistors R1 and R1.

Transistors Q, , Q1゜, Qll constitute a current mirror circuit, and transistor Ql! + Qts rQ1
4 also constitutes a current mirror circuit. In addition, the transistor QI5 + Qlm is a current collector circuit C8,
The transistor Qsv J Qlm similarly constitutes a current mirror circuit, and each of these current mirror circuits operates as an output circuit of the quad 2-chair detector. When the node N1 is, for example, at a high level and the node N is at, for example, a low level, 8-character detection waveforms S, , S, as shown in the figure are obtained at points A and B.

What should be noted here is the circuit operation of the circuit block 32.

First, the circuit operation when switch SW is connected to contact a will be described. If the above-mentioned S biopsy wave output S1゜S is obtained and the current change in the current flowing as shown by the arrow is a low frequency or direct current that is close to direct current, what kind of response will occur on the capacitor C connected to point A? Neither. Therefore, resistance R, yoR
Be B, resistance turtle.

The analog summation output, which is the common connection point X of R11, is equal to a constant reference voltage VRICF* and is not affected by the current shown in the direction of the arrow. In other words, the output of operational amplifier A1 is VRIF! L doesn't appear.

Next, we will discuss the circuit operation when the current indicated by the arrow is in the audio frequency band. In this case, the current change at point A is caused by
Bypassed to ND and not transmitted to point X. Therefore,
Operational amplifier AI amplifies the voltage at point B using resistors RB and RC, and resistor R1! ``If RL, an output signal V with the same amplitude and opposite phase as that at point B is obtained at the output terminal Z.Thus, the output signal v in response to the audio signal is obtained at the output terminal Z.
o is obtained from the operational amplifier A.

Then, while the above circuit operation is being performed, the capacitor C
The voltage generated at one end of the
Frequency Control) signal is supplied to the local oscillation circuit 14. In this case, the local signal fL
It is preferable that the frequency of the carrier signal is higher than the frequency of the carrier signal.

On the other hand, when the switch SW is switched to the contact point, the capacitor C operates in the same manner as above for the audio signal appearing at the point B, and in this case, the output signal Vo with the same amplitude and opposite phase as the output terminal ZKA point is generated. is obtained.

Then, while the above circuit operation is being performed, the conductor 9''
The voltage generated at one end of C is supplied to the local oscillation circuit 14 as an AFC signal. In this case, the local signal fL
It is preferable that the frequency of the carrier signal is smaller than the frequency of the carrier signal.

Next, the case where the output signal Vo is supplied to a stereo demodulation circuit (hereinafter referred to as MPX) will be described with reference to FIG. Note that the IC shown on the left side of Figure 3 is the second IC.
It has the same circuit configuration as the IC shown in the figure, and the output signal ■ obtained from terminal 7.

is supplied to an FM repeater circuit 40 shown on the right via a coupling capacitor Cc.

Zener diode Dzr) transistor Q4. .

Q4m T Q4a + resistance R4! , R4! ,R,,
lR, , constitutes a one-turn stabilized power supply circuit 41. The voltage VBII becomes the bias voltage of the amplifier 43 provided as a buffer amplifier, and the voltage VBII becomes the bias voltage of the amplifier 43 provided as a buffer amplifier.
The current transformer component is supplied to a superimposing amplifier 43 as a voltage VBB.

The circuit configuration and circuit operation of the PLL circuit 42, decoder 43, etc. that constitute the stereo demodulation circuit 40 are well known to those skilled in the art, and the demodulated R signal and Lft signal are obtained from the decoder 43.

By the way, according to the above circuit configuration, since the DC voltage level 2 is equal to VREF* as described above, the reference is set to voltage VBy.
When l, bias voltage VB, and voltage VBy*<Vysm, it is good to connect one capacitor Cc as shown. Furthermore, if Vagyt>Via, one capacitor Cc may be connected with its polarity reversed.

[Embodiment 2] Next, a second embodiment of the present invention will be described with reference to FIG. 4.

In this embodiment, the bias voltage V1m is used as the bias voltage of the operational amplifier A1. Therefore, the output signal V can be directly connected to the buffer amplifier 43 without going through a capacitor, and in this case, the FM receiver and stereo demodulation circuit 40 described in the first embodiment can be connected to the same IC. This is effective in reducing the number of pins during configuration.

〔effect〕

(1) Since the FM detection output and the reference voltage are in opposite phases to each other, the S biopsy wave output of either of the above FM detection outputs can be obtained at the DC level based on this reference voltage, so the bias voltage of the stereo demodulation circuit is In relation to this, the number of capacitors that transmit the detection output can be reduced.

(2) According to (1) above, the reference voltage can be made the same as the bias voltage and can be directly connected without using the capacitor.

(3) According to (2) above, the FM detection circuit and the stereo demodulation circuit can be configured in the same IC, and the number of external connection terminals of the IC can be reduced.

(4) According to (3) above, the production cost of the FM receiver can be significantly reduced.

Although the invention made by the present inventor has been specifically explained above based on Examples, it is to be noted that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Not even.

For example, the FM detection circuit is not limited to the quad 2-chire frequency detection circuit, but may have other circuit configurations. Further, the Zener diode stabilized power supply circuit may also be any of various other constant voltage circuits.

[Application field]

In the above description, the invention made by the present inventor has mainly been described with respect to an FM receiver, which is the field of application behind the invention, but the invention is not limited thereto.

For example, it can be used for FM channels.

The present invention can be used for at least all electronic devices that perform FM detection.

Simple meA of drawings
.

FIG. 1 shows a block diagram showing the connection relationship between an FM detector and a stereo demodulation circuit, which was considered prior to the invention of the present invention, and FIG. 2 shows a circuit diagram of an FM receiver showing a first embodiment of the invention. , FIG. 3 shows a circuit diagram showing the connection relationship between the FM detector and the stereo demodulation circuit, and FIG. 4 shows a circuit diagram showing the connection relationship between the FM detector and the stereo demodulation circuit according to the second embodiment of the present invention. It is a diagram.

S,,S,... 8-character detection output, V...output signal,
RAI R11l RC...Resistor, A, m operational amplifier, VRIF.

...Reference voltage, VBB ...Bias voltage, SW
...Switch, Cmu, Cc...Capacitor, 30.
・・Phase shifter, -1 cm

Claims (1)

[Claims] 1. Selectively remove the alternating current component of one of the FM detection outputs supplied in opposite phases, and remove the AC component of the other FM detection output.
a switch circuit for transmitting the detection output; an addition circuit for adding one FM detection output from which the alternating current component has been removed and the other FM detection output; and an addition circuit for superimposing the output signal of the addition circuit on a desired bias voltage. An FM receiver comprising an amplifier circuit for amplifying and supplying the amplified information to a next-stage FM stereo demodulation circuit and others.