JPS61200716A - Signal switching circuit - Google Patents

Abstract

PURPOSE:To switch the mode automatically to the stereo reception mode when no SAP signal exists by adding a switching circuit comprising two transistors (TRs). CONSTITUTION:When an SAP detection circuit 36 detects no SAP signal, a TR 1 forming a switching circuit is turned on and a TR 2 is turned off. Thus, a current mirror circuit comprising TRs 3,4 is not activated. Thus, no current is fed to the switching circuit comprising the TRs 5, 6, a voltage at an SAP mode switching voltage output terminal 19 is fixed to a low level and independent of on/off of the switch 21. On the other hand, the input of the current mirror circuit comprising TRs 9, 10 is connected to a collector of the TR 1, then the TR 9 is turned on and activated to bring the potential at a stereo mode switching voltage output terminal 20 to a high level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal switching circuit, and in particular, in an audio multiplex broadcast receiver, stereo reception mode and 8AP (Second
This relates to a switching circuit for receiving mode (Audio Program).

[Conventional technology]

For example, the television audio multiplex broadcast system in the United States uses a main signal (L + R signal) corresponding to the conventional monaural audio part and a sub-signal that is suppressed carrier amplitude modulated with a center frequency of 2fu (fH is the horizontal synchronization frequency). The signal (L-R signal), the presence of the sub-signal, and the frequency that is the reference phase for demodulating the sub-signal (Irot signal, and the frequency modulated signal with a center frequency of 5fH and a frequency deviation of ±10kHz). SAP
Signal (5econdAudio Program signal/
. . . second audio signal) are combined and transmitted as audio output.

The receiver (or receiver) reproduces the right signal (R signal) and left signal (L signal) from the main signal, sub signal, and pilot signal, and outputs audio from the right and left speakers, respectively, for stereo playback. You can enjoy it. Furthermore, the SAP signal can be FM-detected and output as audio from a speaker independently of the stereo reception. Normally, SAP signals are often audio broadcast in a foreign language other than English. Here, considering general use, the receiver is equipped with one right speaker and one left speaker, and is configured to switch between stereo reception and SAP reception by switching a switch. Furthermore, since stereo broadcasting and SAP broadcasting are not always carried out, conventional monaural reception is of course possible. During stereo reception, R and L signals are output from the right and left speakers, respectively, and during monaural reception, monaural signals (L+R signals) are output from the right and left speakers.

As a signal switching circuit for switching between the respective reception modes as described above, a circuit shown in FIG. 3 has conventionally been used. In FIG. 3, the emitters of the PN)') transistor s and the PNP transistor 6 are connected in common to a constant current source 23, and the pace of the PNP transistor 5 is connected to a constant voltage source 17 by weakening the resistor 11, and The collector of the PNP transistor 5 is connected to the reference potential through the series circuit of the resistor 12 and the switch 21, and the collector of the PNP transistor 5 is connected to the reference potential through the resistor 22, and is used as the SAP mode switching voltage output terminal 19, and the pace of the PNP transistor 6 is constant.
It is connected to the voltage source 18, the collector is connected to the reference potential through the resistor 13, and the stereo mode switching voltage output terminal 2
It is set at 4.

In the circuit shown in FIG. 3, the base potential of the transistor 60 is fixed by the constant voltage source 18, and the base potential of the transistor 50 is changed by turning on and off the switch 21, thereby determining the potential of the respective mode switching voltage output terminals 19 and 24. and switches between stereo reception mode and SAP reception mode.

[Problem that the invention seeks to solve]

In a receiver using the conventional signal switching circuit as described above, when the switch is set to SAP reception mode, the receiver performs FM detection on the SAP signal, amplifies it, and outputs it from the speaker. If you receive a stereo broadcast or monaural broadcast that is not available, the S
Only the residual noise of the AP signal detection circuit is output.

That is, when receiving SAP broadcasts in 8AP reception mode and the broadcast changes to stereo or monaural broadcasting, there is a drawback that the reception mode changeover switch must be reset.

[Means for solving problems]

The signal switching circuit of the present invention includes a first switching circuit and a second switching circuit, each having complementary current outputs, and a first . It has second and third current mirror circuits, the first switching circuit has an input as the first switching signal input terminal, one of the complementary current outputs is connected to the input of the first current mirror circuit, and the other is connected to the input of the first current mirror circuit. The second switching circuit is connected to the input of the third current mirror circuit together with the output of the second current mirror circuit, and the second switching circuit has the input as the second switching signal input terminal, and one of the complementary current outputs is connected to the input of the third current mirror circuit. the other is connected to the input of the second current mirror circuit, and the output t of the first current mirror circuit is connected to the current supply leakage of the second switching circuit, and the g
The output of the current mirror circuit No. 3 is used as the second city/multiplier output.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the figure, parts equivalent to those in FIG. 3 are given the same symbols.

In FIG. 1, the SAP detection circuit 36 outputs a low level τ when an 8AP signal is detected, and outputs a low level τ when no SAP signal is detected. NPN
Transistor 1.2 constitutes a first switching circuit,
The emitter of each transistor is connected to the constant current source 15 with the emitter connected to the constant current source 15. The pace of transistor 1 is connected to the output of SAP detection circuit 36 as a first switching signal input terminal, and the collector of transistor 2 is connected to PNP) is connected to the input of the first current mirror circuit composed of transistors 3 and 4, and the collector Vi of transistor 1 is
, PNPh transistors 9 and 8 are connected to the output of the second current mirror circuit aX, and connected to the input of the third current mirror circuit composed of the PNP transistors 9 and 10. On the other hand, the PNP transistors 5 and 6 constitute a second switching circuit, and the emitters of each transistor are common.
The current of is connected to the output of the circuit! The collector of the transistor 5 is connected to the reference potential via the load resistor 13 and forms the SAP mode switching voltage output terminal 19 which is the first control signal output, and the collector of the transistor 6 is connected to the reference potential through the load resistor 13. It is connected to the input of the current mirror circuit. The output of the third current mirror circuit is connected to a reference potential via a load resistor 14', and serves as a stereo mode switching voltage output terminal 20 which is a second control signal output.

Now, if the SAP detection circuit 36 detects the SAP signal gold,
In the first switching circuit, the transistor 2 is turned on and the first current mirror circuit operates, and the second switching circuit performs the same operation as the circuit shown in FIG. 3 described above. That is, by turning on and off the switch 21, the complementary potentials of the respective mode switching voltage output terminals 19 and 20 are determined, and the stereo mode switching voltage output terminals 19 and 20 switch between the stereo reception mode and the SAP reception mode. The terminal 200 phase connects the collector output of the transistor 6 of the second circuit.

Needless to say, the phase is the same as that of the stereo mode switching voltage output terminal 240 in FIG. 3, just through the second and third current mirror circuits.

Next, if the SAP detection circuit does not detect 5AP (i-Q), the first switching circuit turns on transistor 1 and turns off transistor 2. Therefore, the first current mirror circuit does not operate. Therefore, no current is supplied to the second switching circuit, and the potential of the SAP mode switching voltage output terminal 19 is fixed at a low level l/mini, and the n1 switch 21 is turned on and off. The input of the current mirror circuit is connected to the collector of the transistor 1, and the transistor 9 is turned on to operate, and the potential of the stereo mode switching voltage output terminal 20 is set to a high level.

That is, in the signal switching (b) path of the present invention, when SAP broadcasting is being performed, the second switching circuit is enabled by the output from the SAP detection circuit, and by turning on and off the switch 21, stereo reception is performed. If all switching between mode and 5AFE mode is possible and SAP broadcasting is not being performed, the output from the SAP detection (b) path causes the second switching circuit to disable operation τ, and switch 21
Regardless of whether it is on or off, it switches to stereo broadcast reception mode.

FIG. 2 is a circuit diagram showing another embodiment of the present invention;
This is the circuit shown in the figure with a stereo and monaural mode switching circuit added. In the figure, parts equivalent to those in FIG. 1 are given the same symbols.

As shown in FIG. 2, the pilot signal detection circuit 37 is a circuit that outputs a high level when a pilot signal is detected, and outputs a low level when a pilot signal is not detected. PNP transistors 32, 33 and 34 are the third
The switching circuit consists of a switching circuit, which is connected in common to the emitter of each transistor and connected to the output of a third current mirror circuit, and the collector of the transistor 32 is connected to a reference potential via a load resistor 14. At the same time, there is no stereo mode switching voltage output terminal 20e, which is the second cutter 1II41 color number output, and the transistor 330 pace detects the pilot signal [! l! The base of the transistor 34 is connected to the bias power supply 29 through a resistor 27 and to a reference potential through a series circuit of a resistor 26 and a switch 30. The collectors of the transistors 33 and 34 are connected in common, and are connected to a reference potential via a load resistor 25.
control (the monaural mode switching voltage output terminal 31 is connected to the No. 8 output).

If there is no stereo broadcast color code, that is, there is no SAP signal, or even if there is a SAP signal, the switch 21
is off and the potential of the SAP mode switching voltage output terminal is at a low level, and if there is a Pyro or Togo signal, the output of the Pyro Hg signal detection circuit is still at the level, so the transistor 33 of the third switching circuit is The mode is switched between distereo and monaural by turning the switch 300 on and off. That is, when the switch 30 is on, the transistor 34 is turned on, the potential of the monaural mode switching voltage output terminal 31 is still at the level, and the stereo mode switching voltage output terminal 20 is still at the same level.
When the 0 potential is at a low level, the mode becomes monaural mode. However, when the switch 30 is off, the transistor 32 is turned on, the potential at the monaural mode switching voltage output terminal 31 is at a low level, and the potential at the stereo mode switching voltage output terminal 20 is at one level, resulting in a stereo mode.

However, if there is no pilot signal, the output of the pilot signal detection circuit will be at a low level, and this low level will be caused by the two transistors 32.
Since the potential is set lower than the potential applied to the pace of 34, the transistor 33 is turned on and the switch 30 (/, 1
Regardless of whether it is on or off, the potential of the monaural mode switching voltage output terminal 31 is set to a high level, and the potential of the stereo mode switching voltage output terminal 20 is set to a low level to enter the monaural mode.

In other words, even if the mode is set to stereo broadcast reception mode, when the broadcast becomes monaural and the pilot signal disappears, the switch from stereo mode to monaural mode is automatically performed.0 [Effects of the Invention] As explained above, the invention is based on adding a first switching circuit consisting of two transistors to the conventional signal switching circuit. This eliminates the unpleasant situation where only the residual noise of the SAP signal detection circuit is output from the speakers, and automatically switches to the stereo reception mode.

[Brief explanation of the drawing]

FIGS. 1 and 2(2) are circuit diagrams showing the implementation of the signal switching circuit of the present invention, and FIG. WIJ3 is a circuit diagram showing an example of a conventional signal switching circuit. 1.2, 3, 4, 5.6, 7, 8, 9.10, 32, 3
3.34...Transistor, 11, 12, 13
, 14, 22, 25° 26.27...Resistance, 1
5.23... Constant current source, 16°17.18,2
8.35--constant voltage source, 19, 20, 24°3
1...Control voltage output terminal, 36...8
AP detection circuit, 37...Pilot signal detection circuit.

Claims (1)

[Claims] It consists of a first switching circuit and a second switching circuit, each having complementary current outputs, and first, second, and third current mirror circuits, and the first switching circuit receives an input as a first switching signal input. one of the complementary current outputs is connected to the input of the first current mirror circuit, the other is connected together with the output of the second current mirror circuit to the input of the third current mirror circuit, and one of the complementary current outputs is connected to the input of the third current mirror circuit, while the second switching circuit has an input as the second switching signal input terminal, derives the first control signal output from one of the complementary current outputs, connects the other to the input of the second current mirror circuit, and A signal switching circuit characterized in that an output of a first current mirror circuit is connected to a current supply end, and a second control signal output is derived from an output of the third current mirror circuit.