JPS59172847A - Stereo demodulator - Google Patents

Abstract

PURPOSE:To attain the operation at a low voltage by feeding an intermittent current formed by a switching signal to a differential amplifier separating a stereo composite signal into left and right signals as a driving current. CONSTITUTION:The stereo composite signal voltage from a signal source 96 is converted into a current signal by a voltage current converting circuit 90 and controls the operating current of the differential amplifiers 2, 4 demodulating a stereo signal by current inverting circuits 98, 100, 102, 104 and 106. The amplifiers 2, 4 repeat alternately the conduction and nonconduction by a switching signal inputted to terminals 164, 166 by switching circuits 92, 94, separate the stereo composite signal into left and right stereo signals and output respectively them to output terminals 46, 52. Since the circuits 92 and 94 give the intermittent current in response to the switching signal to the amplifiers 2 and 4, the voltage loss is suppressed a low voltage drive is attained. Further, the fluctuation in the DC potential of the stereo demodulation output is prevented and the accuracy of the demodulated output is improved.

Description

Detailed Description of the Invention The present invention provides a stereo demodulator that separates left and right stereo signals from a stereo composite signal using a 38 kHz switching signal that is multiplied by the frequency (19kllz) of a pilot signal in the stereo composite signal. Regarding.

FIG. 1 shows a conventional stereo demodulator.

This stereo demodulator is equipped with a pair of differential amplifiers 2.4 that alternately perform switching operations using switching signals (38 kHz) obtained by multiplying the pilot signal (19 kHz) included in the stereo composite signal. . That is,
The first differential amplifier 2 is composed of a pair of transistors 6.8 having a common emitter, while the second differential amplifier 4
is composed of transistors 10 and ]2 having a common emitter. A switching voltage is applied from the drive circuit 14 to the base of the transistor 6.12, and a switching voltage is also applied from the drive circuit 14 to the base of the transistor 8.10. Also,
A third differential amplifier 18 is installed in each of the differential amplifiers 2.4 to control the operating current thereof using a stereo composite signal. This differential amplifier 18 consists of a pair of transistors 2o, 22 and a resistor 2o.
4.26, an input terminal 28 for a stereo composite signal is formed at the base of the transistor 20,
A bias input terminal 30 is formed at the base of the transistor 22 . In addition, each differential amplifier 2.4.18 is connected between the midpoint of the resistor 24.26 and the reference potential point (GND).
A transistor 32 constituting a constant current source for drawing an operating current is inserted with the reference potential point side as an emitter, and an input terminal 34 for applying a constant bias is formed at the base of this transistor 32. There is.

The output of each differential amplifier 2.4 is generated individually at the collector of transistor 6.10 and transistor 8.12, and each output is generated by a current inverting circuit 38 inserted between the collector of transistor 6.10 and the power supply terminal 36. or transistor 8.
The current is taken out through a current inverting circuit 40 inserted between the collector of No. 12 and the power supply terminal 36. That is, the current inversion circuit 38 is composed of transistors 42 and 44, and an output terminal 46 is formed at the collector of the transistor 44. Further, the current inverting circuit 40 is composed of transistors 48 and 50, and the collector of the transistor 50 has an output terminal 52.
is formed.

Further, between the collector of the transistor 6.10 and the reference potential point, a transistor 54 whose base is commonly connected to the transistor 20 is inserted with the reference potential point side as the emitter and via a resistor 56. 8.
A transistor 58 is inserted between the collector of No. 12 and the reference potential point, with the emitter facing the reference potential point side and a resistor 60 on the emitter side.

The drive circuit 14 connects a resistor 62.64 between the power supply terminal 36 and the reference potential point, and connects a resistor 66.68 and a transistor 70 between the midpoint of this resistor 62.64 and the reference potential point. At the same time, resistors 72 and 74 and a transistor 76 are also connected. transistor 70
．． 76 is an input terminal 78.8 that provides a switching signal.
0 is formed, and a switching signal obtained by multiplying the pilot signal of the stereo composite signal is provided. The switching voltage generated at the midpoint of the resistor 62.64 is then applied to the base of the transistor 6.12, and the switching voltage generated at the midpoint of the resistor 66.68
The switching voltage generated at the midpoint of the l-transistor 8
．． Given on a base of 10.

According to such a configuration, 3
Since an 8 kHz switching signal is applied, transistors 70 and 76 alternately turn on and off in response to the switching signal. As a result, the resistance is 66.68
The switch notching voltage generated at the midpoint of transistor 8
．． 10, while the switching voltage generated at the midpoint of resistor 72.74 is applied to transistor 6.12 to provide switching action.

In this state, when a stereo composite signal is applied to the input terminal 28, the switching operation of the differential amplifiers 2.4 is synchronized to 38 kHz, so that the switching operation of each differential amplifier 2.4 is synchronized to 38 kHz.
The operating current flowing through 4 responds to the operation of the differential amplifier 18,
As a result, the left and right stereo signals are separated from the stereo composite signal, and each output terminal 46, 52 can individually take out the left and right stereo signals.

However, the drive circuit 14 for driving the first and second differential amplifiers 2.4 divides the voltage Vcc applied between the power supply terminal 36 and the reference potential point, and intermittents this by the switching signal. Because of this structure, the voltage loss is large and it is impossible to operate at a low voltage of about 1.5 square meters, and battery-powered devices have drawbacks such as high battery consumption.

An object of the present invention is to provide a stereo demodulator that can operate at a low voltage, for example, about IV.

The present invention includes a switching circuit that generates an intermittent current in response to a switching signal, and the intermittent current generated in the switching circuit is given as a control input,
It is characterized in that it is composed of a pair of differential amplifiers whose operating currents are continuously controlled by a stereo composite signal.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 2 shows an embodiment of the stereo demodulator of the present invention, in which the same parts as in the circuit of FIG. 1 are given the same reference numerals. In the figure, this stereo demodulator is configured with a voltage-to-current conversion circuit 90 in which the third differential amplifier 18 of the stereo demodulator in FIG. a switching circuit 9 that generates an intermittent current in response to a switching signal to drive the drive circuit 14;
2.94.

The voltage-current conversion circuit 90 includes current inversion circuits 98, 100, . 102.104.
106 are installed.

The current inverting circuit 98 is composed of transistors 108 and 110. The bases of each transistor 108 and 110 are connected in common, and the transistor 108 has a diode configuration with a common base and collector. The emitter of the transistor 108 is connected to the power supply line, the constant current source 114 is connected between the collector and the reference potential point together with the signal source 96, and the transistor 11
The emitter of 0 is connected to the power supply line.

The current inversion circuit 100 is a transistor 54.58.116
．． 118.120 and resistance 56.60.122.124
．． It consists of 126. A transistor 116 having a diode configuration with a common base and collector is inserted on the emitter side via a resistor 122 between the collector of the transistor 110 and a reference potential point. The bases of the transistors 54, 58, 116, 118, and 120 are connected in common, and the transistor 118 is inserted between the current inverting circuit 102 and the reference potential point via a resistor 124 on the emitter side. A resistor 12 is installed on the emitter side between the differential amplifier 2 of 1 and the reference potential point.
It is inserted through 6.

The current inversion circuit 102 is composed of transistors 128 and 130, and the transistor 128 has a common base and collector and is configured as a diode. transistor 128
．． The bases of the transistors 130 are commonly connected, and the emitters of the transistors 130 are commonly connected to the power supply line, and the collectors of the transistors 130 are connected to the current path on the second differential amplifier 4 side.

A current inversion circuit 104 is installed corresponding to the current inversion circuit 98 and sets a reference current on the differential amplifier 4 side. That is, in order to independently set a constant current, the current inverting circuit 104 is composed of transistors 132 and 134. The emitters of the transistors 132 and 134 are commonly connected to the power supply line, and the bases of the transistors 132 and 134 are commonly connected to the power supply line. are configured as diodes with a common base and collector. A constant current source 136 that sets a reference current is inserted between the base and collector of the transistor 132 and a reference potential point.

Further, the current inverting circuit 106 includes transistors 138.14
0.142 and resistor 144.146.148. That is, the transistor 138 has a common base and collector and is configured as a diode, and the transistor 138 has a common base and collector.
34 and a reference potential point via a resistor 144 on the emitter side. transistor 138
．． 140 and I42 have their bases connected in common, and each 1-transistor 140.14.2 is connected by individually inserting a resistor 146.148 on the emitter side between the second differential amplifier 4 and the reference potential point. has been done.

The switching circuit 92 is configured by connecting a transistor 150, a resistor 152, and a transistor 154 between the power supply terminal 36 and the reference potential point, and one switching circuit 94 is connected between the power supply terminal 36 and the reference potential point. transistor 156, resistor 158 and transistor 16
It is configured by connecting 0. Transistor 150.1
56 bases have an input terminal 16 that provides a common bias.
2 is formed, and the base of the transistor 154.160 is provided with an input terminal 164.1 for applying a switching signal.
66 is formed.

The operation will be explained based on the above configuration. Input terminal 1
When a switching signal is applied to transistors 64 and 166, transistors 154 and 160 perform a switching operation, and a switching drive current is applied to the base of transistor 6.12 from the collector of transistor 156, and the base of transistor 8.10 receives a switching drive current. A switching drive current is provided from the collector of transistor 150. For each drive current, the L transistors 154 and 160 are switched alternately, and conduction and non-conduction occur selectively, so that the operation of the differential amplifier 2.4 is also responsive to this.

In this way, when the switching operation is performed using an intermittent current in response to a switching signal, voltage loss (rl'I) can be controlled and low voltage driving becomes possible, compared to conventional voltage driving.

Furthermore, in this way, since there is no fluctuation in the input voltage of the differential amplifier 2.4, it is possible to prevent the DC potential of the stereo demodulated output from swinging due to the switching signal, and it is possible to improve the accuracy of the stereo demodulated output.

Also, unlike conventional stereo demodulators, this embodiment
Since the operating current of the differential amplifier 2.4 is converted from a stereo composite signal into a current by the voltage/current conversion circuit 90, low voltage driving is possible.

To explain this operation, it is assumed that no signal is applied from the signal source 96, and the potentials and currents at points A and B in the figure are set to the same value. At this time, when current ■ flows through transistors 1 to 108, a similar current r flows through transistor 110 due to the current mirror effect, and this current The operating current also flows through the dynamic amplifier 2. Further, this current I is passed from the transistor 11B to the transistor 140.1 via the current inverting circuit], 02.
Forced to be given to 42 people.

On the other hand, on the B point side, a similar current flows through the transistor 132.
flows through the transistor 138 due to the current mirror effect, and this current I flows through the transistor 138 due to the current mirror effect.
8 to transistor 140 by the current mirror effect.
．． 142 respectively. In other words, since the transistors 140 and 142 are connected in parallel, their current sinking ability is twice the current I (2I), and since the current ■ is applied from the transistor 130, the second differential amplifier Similarly to the first differential amplifier 2, the operating current 1 is applied to the differential amplifier 4. That is, when the current and potential at points A and B are the same, the operating currents given to each differential amplifier 2.4 have the same value, and therefore, the signal given from the signal source 96 causes the transistors to 108 with the type i
'i? Assuming that a current of 1.51 flows with respect to fl, a current of 4; J: 1.51 flows in the first differential amplifier 2 due to the current mirror effect of the current inversion circuit 98. From the inverting circuit 102 to the transistor 14
A current of 1.5I is applied to the collector side of 0.142.

On the other hand, since the current I is set in the current inversion circuit 104 by the constant current source 136, the current r is given from the transistor 138 to each transistor 140 and 142, and the combined value is the current of 2I. Having the ability to absorb is heartwarming.

However, since the current of 1.5I is applied from the transistor 130, these left ventricular flow components 21-],
A current of 51 = 0.5I will flow through the second differential amplifier 4G, and the operating currents of the first and second differential amplifiers 2.4 will be 1.5■ and 0.5■, respectively. current I
It makes a difference. That is, since different operating currents are given to each differential amplifier 2.4 according to the signal from the signal source 96 with respect to the reference value as described above, the current is equivalent to that of a conventional voltage-operated differential amplifier. Generally, a current-operated differential amplifier is configured with a voltage-current conversion circuit 90. Therefore, the differential amplifier 2.4
is excited by the stereo composite signal to be demodulated, and each differential amplifier 2.4 can separate left and right stereo signals from the stereo composite signal, and each output terminal 46.5
2, left and right stereo signals are taken out individually.

Further, in such a stereo demodulator, the operating voltage between the power supply terminal 36 and the reference potential point is different from the conventional stereo demodulator shown in FIG.
Forward drop voltage VF, +-rangistaro, 8.10.
12 collector-emitter voltage VCEI,) Ranjisk 54.58.116.118.120.140,14
2 collector-emitter voltage VCE2 and resistor 56.
60.122.124.126 common voltage rise V11 composite value Vc c (=Vp→-VCEI +VCE2
+VR), and the minimum operating voltage can be lowered.

Ru. That is, good operating characteristics can be obtained even if the power supply voltage VCC applied to the power supply terminal 36 is lowered, and operation can be performed at a voltage as low as about 1.5V.

Furthermore, if the voltage applied to the power supply terminal 36 is set to the same value as in the conventional circuit, a wide range can be achieved, and in particular, even if the battery voltage decreases due to battery consumption, the operating characteristics will not fluctuate. Stable operating characteristics can be obtained without causing any signal distortion, and good stereo demodulation is possible without signal distortion.

As explained above, according to the present invention, an intermittent current formed by a switching signal is given as a drive current to a differential amplifier for separating left and right stereo signals from a stereo composite signal, which is different from conventional voltage drive. Compared to conventional batteries, the reactive voltage can be reduced to suppress voltage loss, the minimum operating voltage can be lowered, and in the case of battery drive, battery consumption can be kept low.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional stereo demodulator, and FIG. 2 is a circuit diagram showing an embodiment of the stereo demodulator of the present invention. 2... First differential amplifier, 4... Second differential amplifier, 92.94... Switching circuit.

Claims (1)

[Claims] A switching circuit that generates an intermittent current in response to a switching signal, and a pair of differential amplifiers that receive the intermittent current generated in this switching circuit as a control input, and whose operating current is continuously controlled by a stereo composite signal. A stereo demodulator comprising: