JPS606897Y2 - Recording/playback switching circuit - Google Patents

Description

[Detailed explanation of the invention] This invention is based on VTR (video tape recorder), etc.
The present invention relates to a switching circuit between a recording state and a reproduction state.

Conventionally, a recording/reproduction switching circuit 2 for a video tape recorder as shown in FIG. 1 has been known.

That is, in FIG. 1, 1 is a recording amplifier, the output side of this amplifier 1 is connected to the primary winding 2a of the output transformer 2, and one end of the secondary winding 2b of the output transformer 2 carries a large current. The other end is connected to the collector of the transistor 3 to be obtained, and the other end is grounded.

Further, the base of the transistor 3 is connected to a recording switching signal input terminal 5 via a resistor 4 and grounded via a capacitor 6.

The emitter of this transistor 3 is connected to one end of the secondary winding 7b of the rotary transformer 7, and the other end of the secondary winding 7b of this rotary transformer 7 is grounded, and the primary winding 7a is used for both recording and reproduction. is connected to a rotating magnetic head 8.

Further, one end of the secondary winding 7b of the low retransistor 7 is further connected to the primary winding 10a of the input quadrature transformer 10 of the regenerative amplifier 9.
connected to one end of the

The collector-emitter of a switching transistor 11 is connected between the other end of the primary winding 10a of the input transformer 10 and the other end of the secondary winding 7b of the rotary transformer 7. The base is connected to a reproduction switching signal input terminal 13 via a resistor 12 and grounded via a capacitor 14.

One end of the secondary winding 10b of the input quadrature transformer 10 is connected to the input end of the regenerative amplifier 9, and the other end of the secondary winding 10b is grounded.

Note that 1a is a recording signal input terminal, and 9a is a reproduction signal input terminal.

In the above-described circuit, during recording, the recording switching signal applied to the terminal 5 becomes high level, and the transistor 3 becomes conductive.

A recording signal from the recording amplifier 1 is supplied to the magnetic head 8 through this transistor 3 and recorded.

Next, during reproduction, the reproduction switching signal applied to the terminal 13 becomes high level, and the transistor 11 becomes conductive.

A reproduction signal from the magnetic head 8 is supplied to the reproduction amplifier 9 via the transistor 11 and the transformer 10.

By the way, in the circuit shown in FIG. 1, the regenerative amplifier 9
The input quadrature transformer 10 is normally tuned to the upper limit of the carrier wave frequency, but since the other end of the secondary winding 7b of the rotary transformer 7 is grounded both during recording and reproduction, the rotary transformer 7 When the cable between the input quadrature transformer 10 and the input quadrature transformer 10 becomes longer, the tuning frequency of the input quadrature transformer 10 decreases due to the capacitance between this cable and the ground.
This has the disadvantage that the playback output level decreases, and the cable also has the disadvantage that it easily picks up noise carried by the ground.

Furthermore, since the transistor 11 is connected in series to the output of the head 8 during reproduction, there is a drawback that the S/N ratio deteriorates.

Therefore, a recording/reproduction switching circuit as shown in FIG. 2 was devised to eliminate the above-mentioned drawbacks.

That is, in this example, both ends of the secondary winding 7b of the rotary transformer 7 are directly connected to both ends of the primary winding 10a of the input transformer 10.

One end of the secondary winding 10b of this input transformer 10 is connected to the input end of the regenerative amplifier 9, and is also grounded through the collector emitter of a transistor 15. It is connected to the input terminal 5, and the connection point between the resistor 16 and the base is grounded via the capacitor 17.

Further, the other end of the secondary winding 10b of the input quadrature transformer 10 is directly connected to one end of the output transformer 2, and the connection point thereof is grounded through the collector emitter of a transistor 18. It is connected to the reproduction switching signal input terminal 13, and the connection point between this base and the resistor 19 is grounded via a capacitor 20.

The rest of the structure is the same as in FIG.

In this example configured in this way, when recording,
The transistor 15 is turned on by the recording/reproduction switching signal.
The transistor 18 is turned off, and the recording signal from the recording amplifier 1 is supplied to the head 8 through the output transformer 2 and the input transformer 10.

On the other hand, at this time, the regenerative amplifier 9 includes a transistor 15.
is on, the recording signal is muted and not supplied through this transistor.

During reproduction, the switching signal turns off the transistor 15 and turns on the transistor 18, and the signal reproduced by the head 8 passes through the input transformer 10 to the reproduction amplifier 9.
supplied to

In the case of the circuit shown in FIG. 2 configured in this way, during playback, neither one end nor the other end of the primary winding 10a of the input transformer 10 is grounded, so a capacitance exists between the cable and the ground. This eliminates the drawbacks of the circuit shown in FIG.

Incidentally, since no transistor is connected in series with respect to the reproduction output of the head 8, deterioration of the S/N ratio is also reduced.

In addition, in this example, the recording signal is supplied to the head 8 via two transformers 2 and 10, but eliminating both transformers 2 and 10 is as follows. Not possible for some reason.

That is, in order to reduce noise, the regenerative amplifier 9 is made of FE.
A T amplifier is used, but this FET amplifier has a high input impedance.

Therefore, a matching transformer 10 is required.

Further, the recording input voltage of the head 8 is normally 4V, but
If the winding ratio of the transformer 10 is, for example, head side winding: reproducing amplifier side winding = 1:4, the output of the recording amplifier 1 will be about 16V.

However, this is not possible and a step-up transformer 2 is required.

However, when the recording signal is supplied to the head 8 through two transformers in this manner, the phase rotation of the sideband components of the recording signal becomes large and the low-frequency characteristics deteriorate.

This is because when the recording signal is a color video signal, the carrier color signal has been subjected to low-frequency conversion, resulting in a disadvantage that the carrier signal component deteriorates.

In addition, in order to lower the resistance value of each switching transistor when it is on, a large base current must flow; however, in the case of the circuit shown in Figure 2, the recording current flows directly into the transistor 15 during recording, so It has the disadvantage of requiring a large base current.

This invention attempts to propose a recording/reproducing switching circuit which can eliminate the drawbacks of the conventional circuits shown in FIGS. 1 and 2 mentioned above.

An embodiment of this invention will be described below with reference to FIG.

The example shown in FIG. 3 is an example in which two rotating magnetic heads are provided and recording signals from the recording amplifier 1 are supplied to these two heads, and 8A and 8B are the rotating magnetic heads, respectively.

In this case, since the recording and reproduction signal systems for each of these heads 8A and 8B are exactly the same, the subscript A is attached to the head 8A, and the subscript B is attached to the head 8B. For example, the recording and reproducing system of the head 8A will be explained, and the explanation of other systems will be omitted.

That is, in this example, one end of the secondary winding 7Ab of the rotary transformer 7A is connected to the primary winding 1QAa of the transformer IOA.
The other end of the secondary winding 7Ab of the rotary transformer 7A is connected to the secondary winding 21b of the recording transformer 21.
Connected to one end of A.

The other end of the primary winding 1QAa of the transformer IOA is connected to the other end of the secondary winding 21bA of the transformer 21.

The output end of the recording amplifier 1 is connected to the recording transformer 21.
The output terminal of the recording amplifier 1 is grounded through the collector emitter of the transistor 22, and the base of the transistor 22 is connected to the reproduction switching signal input terminal 13 through the resistor 23. The connection point 23 is grounded via a capacitor 24.

The rest of the structure is the same as the example shown in FIG. In the circuit configured as described above, during recording, the recording switching signal obtained at terminal 5 rises to a high level, so both transistors 15A and 15B are turned on.
The primary sides of the input transformer 10A and IOB will be short-circuited.

On the other hand, since the reproduction switching signal obtained at the terminal 13 at this time is at a low level, the transistor 22 is turned off, and the recording signal from the recording amplifier 1 is supplied to the heads 8A and 8B through the recording transformer 21.

In this case, transformers IOA and IOB step up the output of heads 8A and 8B, but if their turns ratio is set to N1 (primary side: secondary side), the current flowing to the secondary side is equal to the recording current. becomes 17N□, and transistor 1
5A and 15B require less base current.

Furthermore, the resistances of the transistors 15A and 15B when they are on are converted to (1/N□)2, so they become very small.

Furthermore, in this case, the recording signal is transmitted to the recording transformer 21.
Since the signal is supplied to the heads 8A and 8B through only one signal, deterioration in the low frequency range of the recording signal is reduced.

Next, during reproduction, the recording switching signal becomes low level, and transistors 15A and 15B are turned off.

Then, since the reproduction switching signal becomes high level, the transistor 22 is turned on and the primary side of the recording transformer 21 is short-circuited.

Therefore, signals reproduced by heads 8A and 8B are supplied to regenerative amplifiers 9A and 9B through input transformers 10A and IOB, respectively.

In this case, the recording transformer 21 is for stepping up the recording current, but its turns ratio is 1.
Next side:Secondary side-N2: When the ratio is 1, the impedance seen from the head side is (1/N2)2 of the resistance value when the transistor 22 is on, which is very small.

Therefore, deterioration of S/N during reproduction is reduced.

As described above, according to this invention, the drawbacks of the conventional recording/reproduction switching circuits shown in FIGS. 1 and 2 can be effectively eliminated.

In addition, in this invention, the input transformer of the regenerative amplifier may be omitted.

[Brief explanation of drawings]

1 and 2 are connection diagrams of conventional examples of this devised circuit, and FIG. 3 is a connection diagram of an example of this devised circuit. 1 is a recording amplifier, 5 is a recording switching signal input terminal, 7 is a rotary transformer, 8A, 8B are rotating magnetic heads, 9 is a reproducing amplifier, 10 is an input transformer thereof, 13 is a reproduction switching signal input terminal, 15A, 15B, and 22 21 is a switching transistor, and 21 is a recording transformer.

Claims (1)

[Scope of utility model registration request] A series circuit of a secondary winding of a recording transformer and a primary winding of an input transformer is connected to the recording/reproducing head, and a first switching element is connected in parallel to the primary winding of the recording transformer, The output end of the recording amplifier is connected, a second switching element is connected in parallel to the secondary winding of the input cadence, and the input end of the reproducing amplifier is connected, and the first switching element is turned off during recording. At the same time, the second switching element is turned on, and the recording current from the recording amplifier is supplied to the recording/reproducing head, and during reproduction, the first switching element is turned on, and the second switching element is turned on. A recording/reproduction switching circuit in which a switching element is turned off and a reproduction output of the recording/reproduction head is supplied to the reproduction amplifier.