JPH0357649B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an electronic switch device suitable for switching between recording and playback in a tape recorder, for example.

In a tape recorder that performs both recording and playback operations, a switch circuit for switching between a recording state and a playback state is essential. In recent years, from the standpoint of improving the performance of equipment, there has been an active movement to digitize this switch circuit.

FIG. 1 shows a configuration diagram of a conventional example of a recording or reproducing circuit for a tape recorder which is an electronic switch circuit. In Fig. 1, 5 and 7 are electronic recording and playback switching switches (hereinafter abbreviated as switches), and in switches 5 and 7, A is a common terminal, and B is a terminal when selecting the playback state. terminal,
C is the terminal when recording state is selected. In this circuit, the flow of the recorded audio signal in the recording state in which the switches A and C of the switches 5 and 7 are in a conductive state and the switches A and B are fixed in a non-conductive state is as follows. That is, the audio signal input through the microphone 3 passes through the amplifier circuit 4, the switch 5, the amplifier circuit 6, and the amplifier circuit 8, is output from the line output terminal 11, and is guided to an audio amplifier or the like.

On the other hand, the output signal of the amplifier circuit 6 is branched,
The signal passes through a switch 7, a recording amplifier circuit 9, and a bias trap peaking circuit 10, is applied to a recording or reproducing head (hereinafter simply referred to as head) 1, and is recorded on a tape by electromagnetic conversion. At this time, the signal to the head 1 is applied to the amplifier circuit 2, and the output signal is output from the amplifier circuit 2, but there is no conduction between the B terminal and the A terminal of the switch 5, to which the output signal from the amplifier circuit 2 is applied. Therefore, the signal from the head 1 has no influence on the amplifier circuit 6 and beyond. Therefore, in such a state, a normal recording function will be exhibited.

On the other hand, in the illustrated circuit, switches 5 and 7
In the playback state in which A and B are fixed in a conductive state and A and C are fixed in a non-conductive state, the audio signal obtained from the tape by magnetoelectric conversion by the head 1 is transmitted to the amplifier circuit 2. , passes through the switch 5 and the amplifier circuits 6 and 8, and is output from the line output terminal 11,
It is guided by audio amplifiers, etc. Note that the signal from the microphone 3 is not output to the output terminal 11 because the terminals A and C of the switch 5 are in a non-conducting state. Furthermore, since the switches A and C of the switch 7 are in a non-conducting state, the output signal from the amplifier circuit 6 passes through the recording amplifier circuit 9 and the bias trap/peaking circuit 10 and is not applied to the head 1. , In such a state, the circuit will exhibit a normal regeneration function.

As mentioned above, in the circuit of Figure 1,
If the switch is fixed in either the playback or recording state, the playback or recording function will function normally. However, problems may occur during the so-called transition period when the switch is switching from recording to playback or from playback to recording. Hereinafter, the invention for this problem will be explained using FIG. 1.

In FIG. 1, for some reason during the transition period when switches 5 and 7 are switching from recording to playback or from playback to recording, the timing of switching between the two is shifted, and the timing between switches 5 and 7 changes. Consider the case where A and C of switch 7 become conductive at the same time. When a mechanical switch is used, the inconvenience of falling into such a state can be easily prevented by setting the switching timing to a break type. However, when the switch is converted to an electronic switch, current switching of a pair of differential circuits is often used to perform the switch operation, and during switch switching, current flows through both pairs of transistors that make up the differential circuit. Therefore, it is easy for the switches 5 and 7 shown in FIG. 1 to become conductive at the same time between A and B and between A and C.

In such a state, as can be seen from FIG. 1, the output of the amplifier circuit 2 is connected to the input of the amplifier circuit 2 through the switch 5, the amplifier circuit 6, the switch 7, the recording amplifier circuit 9, and the bias trap/peaking circuit 10. , a closed loop circuit is constructed. The voltage gain of this closed loop circuit is usually a very large value of 60 dB or more, so if there is a small signal within the closed loop, it will be amplified repeatedly within the closed loop, and eventually a steady oscillation state will occur. Put it away. Since the signal that is the source of this oscillation always exists in the form of thermal noise of elements in the closed loop, such an oscillation state can easily occur. When such an oscillation condition occurs, since head 1 is connected in the closed loop circuit, the oscillation signal undergoes electromagnetic conversion by head 1 and is recorded on the tape, which prevents tape playback. At this time, this recorded oscillation signal causes unnecessary noise.

As described above, in the recording or reproducing circuit as shown in FIG. 1, a problem occurs when the switches 5 and 7 are switched.

As a solution to this problem, various measures have been attempted in the past in electronic switch recording or playback circuits. For example, in the circuit shown in Fig. 1, when switching from the recording state to the playback state by shifting the switching timing of switches 5 and 7, first switch 7 is switched from the recording state with conduction between A and C.
After completely switching to the playback state where A and B are conductive, switch 5 is switched from the recording state where A and C are conductive to the playback state where A and B are conductive, and conversely from the playback state to the recording state. A method has been proposed in which the opposite operation is performed when switching. As a result, between A and B of switch 5 and A and B of switch 7,
This prevents the capacitors from becoming conductive at the same time, and the oscillation state described above can be prevented.

However, in order to realize such an operation, the operating states of the electronic switch must be (1) conductive between A and C of switches 5 and 7, non-conductive between A and B, and (2) non-conductive between A and B of switches 5 and 7.
There is continuity between A and C of switch 5 and A and B of switch 7, and continuity between A and B of switch 5 and A and B of switch 7.
(3) Switches 5 and 7 must be in three states: non-conducting between A and C, and conductive between A and B, and switches 5 and 7 are three-value controlled electronic switches. I needed to. This inevitably makes the electronic switch circuit complicated, and it is also difficult to operate it at a low voltage of several volts or less.

Another solution to the oscillation problem is to install a muting circuit in the loop circuit that causes oscillation, and to use muting to lower the loop gain during switch switching operations to prevent oscillation. Complication was an unavoidable problem.

The present invention was made in view of the above problems.
This is an electronic switch circuit that solves the oscillation problem mentioned above, which is simpler than the previous method, and allows operation at low voltage, as well as a recording and muting function. The purpose is to provide an extremely good electronic switch for switching purposes.

Hereinafter, the present invention will be explained in detail based on the drawings. FIG. 2 shows a block diagram of an electronic switch device for switching between recording and playback according to the present invention. In FIG. 2, parts with the same numbers as in FIG. 1 are constructed in the same way as in FIG. The circuit shown in FIG. 2 according to the present invention differs from the circuit shown in FIG. 1 in that in the conventional example shown in FIG. In contrast, in the circuit shown in FIG. 2 according to the present invention, the switch corresponding to switch 7 in FIG. It is a three-point switching type with two new terminals installed between the terminals.

In the circuit according to the present invention shown in FIG. 2, if the switching timings of switches 5 and 12 are set as shown below, the loop formation when switching between recording and playback, which was a problem in the example of FIG. 1, can be avoided. It is possible to eliminate the problem of oscillation caused by First, when switches 5 and 12 are both switched from the recording state with continuity between A and C to the playback state with continuity between A and B, switch 12 is switched from the state of continuity between A and C to the state where it is switched between A and D. Make it conductive, and then make it conductive between A and B. Then, after the switch 12 becomes conductive between A and D, the timing is set so that the switch 5 is switched from conduction between A and C to conduction between A and B, and terminal D is grounded. ,
In FIG. 2, the output of the amplifier circuit 2 is switched to the switch 5,
This eliminates the formation of an oscillation loop as pointed out in the example of FIG. 1 where the signal is introduced into the input of the amplifier circuit 2 through the amplifier circuit 6, switch 12, recording amplifier circuit 9, and bias trap/peaking circuit 10. The problem of oscillation can be avoided.

Next, contrary to the above, when switches 5 and 12 in FIG. 2 are both switched from the playback state with continuity between A and B to the recording state with continuity between A and C,
When the switch 12 is conducting between A and B or A and D, the switch 5 is switched from A and B to A and C, and then the switch 12 is switched to A and C. By setting the timing, no oscillation loop is formed and the oscillation problem can be avoided.

As described above, by using the circuit shown in FIG. 2 according to the present invention, it is possible to solve the problem of oscillation loop formation when switching between recording and playback, and further, as will be explained in detail in the following specific example. By adopting the above-mentioned switching timing, it is possible to make the switches 5 and 12 substantially binary control type, and it is possible to simplify the circuit, and the switch 5 is able to control the conduction between A and B. It is also possible to easily set the switch 12 to conduction between A and D while in the recording state to perform a recording/mutating operation, and the present invention greatly contributes to the improvement of electronic switch devices for switching between recording and playback. .

FIG. 3 shows an example of a circuit embodying the recording or playback switch 5, 12, amplifier circuit 6, and recording amplifier circuit 9 in the circuit of FIG. 2 according to the present invention.
Hereinafter, the present invention will be explained in detail using FIG. 3.

In FIG. 3, reference numeral 13 denotes a signal input terminal during reproduction, which corresponds to the low terminal of switch 5 in FIG. Reference numeral 14 denotes a signal input terminal during recording, which corresponds to the C terminal of switch 5 in FIG. 15 to 25 correspond to the switch 5 and the amplifier circuit 6 in FIG. 2, and the terminal 26 corresponds to the output terminal of the amplifier circuit 6. Reference numerals 27 to 54 control electronic switch circuits for switching between recording and playback and for controlling recording and muting operations. Terminal 55 is a connection terminal for an external connection switch for switching between recording and playback, 56 is an external connection switch for switching between recording and playback, 57 is a connection terminal for a recording/mutating external connection switch, and 58 is a recording/mutating external connection switch. . 59 to 74 correspond to the electronic switch 12 for switching between recording and playback and the recording amplifier circuit 9 in FIG. 2, the terminal 75 corresponds to the C terminal of the switch 12 in FIG. This corresponds to the output of the recording amplifier circuit 9. 77 is the positive power line, 78 is the negative power line, and 79,8
0 is a power supply and ground terminal.

In the circuit of FIG. 3, of the cases where the recording/mutating external connection switch 58 is connected and in the grounded state, first, the case where the external switch 56 is in the connected state will be described.

In this case, the current of the constant current source 30 is
Since it is directly grounded through the resistor 31, the potential difference between both ends of the resistor 31 becomes zero. Therefore transistor 2
In the differential circuit constituted by 7 and 28, the transistor 28 biased by the constant voltage source 32 becomes active and the transistor 27 becomes inactive, so that the current of the constant current source 29 flows through the diode 34 and the resistor 36. This means that the current flows to the diode 33 and resistor 35 side. Here, if the current flowing through the resistor 36 is set to a value that can sufficiently activate the transistor 38, the transistor 38 and the transistor 22 will be in an active state, and the transistor 41 and the transistor 21 will be in an inactive state.

By the way, since the switch 58 is grounded as mentioned above, the transistors 43 and 44 are inactive, so the collector current of the active transistor 38 generates a voltage across the resistor 39 without affecting the operation. On the other hand, no voltage is generated across the resistor 42 connected to the collector of the inactive transistor 41. If the circuit constants are determined so that the voltage generated across the resistor 39 is higher than the voltage of the constant voltage circuit 47, the differential circuit constituted by the transistors 48, 49, and 50 will only consist of the transistor 48. is in an active state, and transistors 49 and 50 are in an inactive state. Therefore, the current of the constant current source 51 flows to the diode 52 and becomes active, and the diode 5
3 and 54 become inactive. Therefore, a collector current flows through the transistor 67 that forms a current mirror with the diode 52, and on the other hand, the transistor 68 that forms a current mirror with the diode 53 and the transistor 69 that forms a current mirror with the diode 54 both have: No collector current will flow. Therefore, in an electronic switch circuit consisting of three sets of differential circuits composed of transistors 59 to 63, transistor 5
Only the differential circuit composed of circuits 9 and 60 becomes active, and the other two sets become inactive. Therefore, only the signal from the terminal 75 to the base of the transistor 59 passes through the amplifier circuit 70 and comes out as an output to the terminal 76, and the signals to the bases of the transistors 61 and 63 are output from the output terminal. He will not be able to appear on 76. Further, as described above, since the transistor 22 is in an active state and the transistor 21 is in an inactive state, an electronic switch circuit consisting of two sets of differential circuits made up of transistors 15 to 18 is made up of transistors 17 and 18. The differential circuit consisting of the transistors 15 and 16 is inactive, and the signal to the input terminal 14 connected to the base of the transistor 17 passes through the amplifier circuit 25 to the output terminal 26. It will be output as an output signal to. Since the terminal 75 and the terminal 26 are connected, the input signal to the terminal 14 will be outputted to the terminal 76 as an output signal, and the third
In the figure, when the switch 56 for switching between recording and playback is connected, the switches 5 and 12 are both turned on and off in Figure 2.
This is equivalent to the case where conduction occurs between C and C, and the third
The circuit shown in the figure is in recording mode.

Next, as a second case, a case will be described in which the switch 56 for switching between recording and playback is open in FIG. 3. In this case, the current from the constant current source 30 flows into the resistor 31, and a voltage is generated across the resistor 31. If the voltage across this resistor 31 causes the base voltage of the transistor 27 to be higher than the base voltage of the transistor 28, the differential circuit of the transistors 27 and 28 will become The 27 side becomes active. Below, based on the same idea as in the case of the recording state in the first case described above,
If the circuit constants are determined appropriately, transistor 1
The differential circuit of transistors 5 and 16 and the differential circuit of transistors 63 and 64 are activated, and the differential circuit of transistors 17 and 18 and the transistors 59 and 60 are activated.
and the differential circuit of transistors 61 and 62 can both be inactivated,
The signal to the input terminal 13 is output to the output terminal 26 as an output signal, and the signal to the input terminal 14 is not output to the output terminal 26 as an output signal. Further, since the base circuit of the active transistor 63 is grounded in an alternating current manner through the resistors 73 and 74, no signal is output to the output terminal 76.

As described above, when the recording/playback switching switch 56 is open, the switches 5, 12 are
Both are equivalent to the case where A and B become conductive, and the circuit of FIG. 3 is in a regenerating state.

Next, as a third case, a transient state in which the recording/playback switch 56 changes from a connected state to an open state will be described. In this case, transistor 2
The operation of the differential circuit consisting of the transistors 7 and 28 changes from the recording state in which the transistor 28 is active and the transistor 27 is inactive in the first case described above, through a transition period in which both the transistors 27 and 28 are active. , the transistor 28 in the second case described above.
The state changes to a regeneration state in which the transistor 27 is inactive and the transistor 27 is active. Since the recording state and the reproducing state are as described above, a third case will be described in which the transistors 27 and 28 are both in the active state. Transistors 27, 28
In a transient state in which both transistors 27 and 28 are active, the diode 33
The voltages generated across the resistor 35, the diode 34, and the resistor 36 are applied to the transistors 21 and 22, respectively.
is fully activated, and at the same time, transistor 1
During a period when the two differential circuits 5 to 18 are both active and the input signals to the input terminals 13 and 14 are both at the output terminal 26, the constant current source 29, the resistor 35, By appropriately determining the values of 36, 37, and 40, transistors 38, 4
1 is set to a sufficiently lower value than in the first and second recording and playback states described above, and the voltages generated in the resistors 39 and 42 are set to be sufficiently lower than the voltage of the constant voltage source 47. Make it lower. As is well known, there is an exponential relationship between the base-emitter voltage and the collector current of a transistor, and as the base-emitter voltage increases, the collector current increases rapidly. , 41 at a sufficiently low value, the above-mentioned state can be easily realized without contradicting the states described in the first and second cases. In such a state, in the differential circuit made up of transistors 48 to 50, only transistor 49 is in an active state and both transistors 48 and 50 are in an inactive state.
Of the set of differential circuits, only the differential circuit made up of transistors 61 and 62 is in an active state, and the other two sets are in an inactive state. Since the base resistors 71 and 72 of the input transistor 61 of the differential circuit consisting of the transistors 61 and 62 in the active state are grounded in an alternating current manner and set to a no-signal state,
Regardless of the presence or absence of a signal to the input terminal 75, no signal will be output to the output terminal 76.

As described above, according to the electronic switch device of the present invention, which skillfully uses the relationship between the base-emitter voltage and the collector current of the transistors 38 and 41,
In the transient state when the switch 55 changes from the connected state to the open state, a state equivalent to the case where the switch 12 in FIG. 2 becomes conductive between A and D can be realized, and the circuit in FIG. 3 By using this, it is possible to prevent the occurrence of oscillation loops.
Contrary to the case described above, the switch 56 in FIG. 3 can similarly prevent the occurrence of an oscillation loop even in a transient state in which it changes from an open state to a connected state.

Next, as a fourth case, consider a case where the recording/mutating switch 58 is switched from the previously connected state to the open state. In this case, the current from the constant current source 45 activates the transistors 43 and 44, so the voltage generated across the resistors 39 and 42 should be lower than when the transistors 43 and 44 are inactive. I can do it. Under such circuit operating conditions, the base voltage of transistor 49 in the differential circuit made up of transistors 48 to 50 is set to
If the voltage is set higher than both base voltages of transistors 59 to 59, as in the third case,
Of the three sets of differential circuits made up of transistors 64, only the differential circuit made up of transistors 61 and 62 is activated, so no signal is output to the output terminal 76. This operation is possible when the recording/playback switch 56 is in either the playback or recording position, so even when the recording state is selected with the switch 56 and an audio signal is coming to the input terminal 75, the switch 58 can be pressed. By opening it, no signal is output to the output terminal 76, allowing recording and muting operation.

As described above, by using the electronic switch device of the present invention, it is possible to prevent the occurrence of oscillation loops when switching between recording and playback, prevent oscillation problems when switching between recording and playback, and prevent the problem of oscillation when switching between recording and playback. It can also have a muting function. Also,
By using binary control to switch between recording, playback, or recording-mutating operations, it is possible to switch between recording, playback, or recording-mutating operations using the simplest mechanical switch, a so-called one-make external switch. It is possible to improve the reliability and reduce the cost of an electronic switch type recording or playback switching circuit.

Furthermore, as can be seen from FIG. 3, since the number of diodes connected in series in each path existing between the positive power supply line 77 and the negative power supply line 78 is small, the power supply voltage is low, e.g.
Full electronic switch operation is possible even with a power supply voltage of 3V, making it possible to introduce electronic switches into low-voltage equipment.

Further, in the electronic switch device according to the embodiment of the present invention shown in FIG. 3, all the circuit elements are suitable for semiconductor integrated circuits, so
It is also easy to realize the circuit section except for 58 as a semiconductor integrated circuit.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing a conventional example of a recording or playback circuit for a tape recorder that has been converted into an electronic switch.
FIG. 3 is a block diagram showing a recording or reproducing circuit for a tape recorder which is an electronic switch according to the present invention, and FIG. 3 is a circuit diagram showing an embodiment of a switching circuit which is an electronic switch according to the present invention. 1... Recording or playback head, 2, 4, 6,
8...Amplification circuit, 3...Audio input device such as a microphone, 5...First recording or playback switching electronic switch, 7...Second recording or playback switching electronic switch, 9...Recording amplifier circuit , 10... Bias trap/peaking circuit, 11... Line output terminal, 12... Second recording or playback switching electronic switch, 13, 14... Input terminal, 15, 1
6, 17, 18, 27, 28, 48, 49, 5
0, 59, 60, 61, 62, 63, 64...transistor for differential circuit configuration, 19, 20, 65,
66...Current mirror transistor, 21,2
2,67-69...Emitter current supply transistor, 23,24,37,40...Emitter resistor, 25,70...Amplifier circuit, 26...Output terminal, 29,30,45,51...Constant current Source, 3
1, 35, 36, 39, 42, 46, 71-74
...Resistor for base bias generation, 32, 47...
Constant voltage source, 33, 34, 52-54... Diode, 38, 41... Transistor for base bias voltage generation current supply, 43, 44... Transistor for controlling muting operation, 55... Switch for recording or playback switching Connection terminal, 56... Recording or playback switching switch, 57... Recording/mutating switch connection terminal, 58... Recording/muting switching switch, 75... Terminal, 7
6... Output terminal of recording amplifier circuit, 77, 78...
Power line, 79, 80...power terminal.

Claims (1)

[Claims] 1. Each output generation point of the first and second differential circuits is commonly connected to the input terminal of the first signal amplification circuit, and each one of each pair of transistors of the first and second differential circuits is connected in common. A first signal source and a second signal source are each individually connected to the base terminals of the transistors of the first and second differential circuits. a first switch circuit section connected to the output terminal of the first signal amplification circuit at the terminal thereof, and a short-circuit opening/closing switch at one input terminal of the differential amplification circuit configuration; A first control means for driving each switch element for setting each of the first and second differential circuits to an active state, and an input terminal of a second signal amplification circuit by an output signal of The output generation points of the third, fourth, and fifth differential circuits are commonly connected to each other, and the first signal amplification is connected to the base terminal of one of the pair of transistors of the third differential circuit. The output terminals of the circuits are connected to each other, and a fixed potential is applied to the base terminal of each one of the pair of transistors of the fourth and fifth differential circuits, and the third and fourth differential circuits are connected to each other.
and a second switch circuit section in which the output terminal of the second signal amplification circuit is connected to the base terminal of the other transistor of each pair of transistors of the fifth differential circuit; a second control of the differential amplifier circuit configuration that is selected by the output signal of the control means and drives each switch element for setting each of the third, fourth and fifth differential circuits in an active state; An electronic switch device comprising means.