JPS6080104A - Recording and reproducing circuit - Google Patents

Abstract

PURPOSE:To attain the accurate switching between the record and the reproduction with a simple constitution of circuit which can be easily converted into monolithic integration, by obtaining easily the frequency characteristics of a record mode as well as the resonance characteristics of a reproduction mode. CONSTITUTION:In a record mode the emitter of a transistor (TR) Q22 is grounded with the collector connected to and end of a winding 32a of a rotary transformer 32. The other end of the winding 32a is connected to the base of a TRQ23 via a capacitor 34 and receives no effect of the capacity of a circuit at the reproduction side. In a reproduction mode the TRQ22 is used for both a switching TR and a constant current output TR. Thus the use of a bypass capacitor is eliminated and the structure of a changeover switch is simplified. In this way, a recording/reproducing circuit and a switching circuit of a VRT can be converted with high efficiency into a monolithic IC which works at a low level of voltage. The deterioration of frequency characteristics is avoided in a record mode. Furthermore it is possible to obtain easily the desired resonance frequency characteristics without being influenced by the recording circuit side.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a recording/reproducing circuit, and for example, a recording/reproducing circuit that detects a minute voltage signal obtained from a rotating magnetic head in a video tape recorder (hereinafter referred to as v'rn) before reproducing it. This circuit switches the signal tone to supply the recording current signal from the recording output amplification stage to the rotary magnetic head during reproduction.

[Technical background of the invention and its problems] VTR recording generally uses a constant current recording method.

The configuration of the regeneration and its switching circuit is shown in FIG. In FIG. 1, reference numeral 11 denotes a recording signal input terminal, and the input signal is converted into a current by a voltage-current converter 12, amplified by a current amplifier 13, and a recording/reproducing switching circuit 1.
4 to the mouth-tally transformer 15. The output signal of the rotary transformer 15 is then applied to the rotating magnetic head 16.

On the other hand, during VTR playback, the signal picked up by the rotating magnetic head 16 is transferred to the rotary transformer 15. The signal is input to the reproduction preamplifier 17 via the recording/reproduction switching circuit 14 and is led out to the output terminal 18 .

In the case of an output circuit for VTR's constant current recording method, the frequency band is several MHz or more, and the maximum signal current is 20 mAp-p.
degree is necessary. If we attempt to realize the system shown in Figure 1 using a monolithic integrated circuit to satisfy this requirement, N
When a vertical transistor is used as a complementary transistor to a PN) transistor, the performance is not sufficient, and it is necessary to use a single-ended class-A operation circuit using an NPN transistor.

FIG. 2 shows a monoclick integrated circuit system.

Transistors Qll and Q12 constitute a recording output current amplifier, and transistor QI3 is a switching transistor. The recording input signal is input to the terminal 21 and applied to one end of the winding 23a of the rotary transformer 23 via the collector of the transistor QIO. transistor Q
A recording/reproduction switching signal is input to the control terminal 22 of the base 12, which is turned off during recording and turned on during playback.

The recording signal input to the rotary transformer 23 is
3b is supplied to the rotating magnetic head 24 connected to the magnetic head 3b. The other terminal of the winding 23a of the rotary transformer 23 is connected to the power supply 2-in 25. In addition, the capacitor 26
It is grounded via , and is grounded in terms of alternating current.

During reproduction, the signal picked up by the rotating magnetic head 24 is transferred to the rotary transformer 23. It is input to the base of transistor Q13 via coupling capacitor 27. The base of the transistor Q13 is grounded via a trimmer capacitor 28 for resonant frequency adjustment.The transistors Q13 and Q14 are a regenerative preamplification stage υ using a cascode-connected amplifier, and the collector of the transistor QJ4 is connected to a resistor 29. The base is connected to a constant voltage source 30, and the emitter is connected to a transistor Q.
It is connected to 13 collectors. Transistor Q13
The emitter of the transistor QJ5 is connected to the collector of the transistor QJ5, and is also grounded via an external bypass capacitor 31. The transistor Q15 is a switching transistor, and a recording/reproduction switching circuit is input to the control terminal 32 of the base, and is turned on during reproduction and turned off during recording. The transistor Q16 reverse biases the base emitter of the transistor Q13 during recording to prevent the recording current from being pumped between the base and emitter of the transistor Q15 during recording, thereby increasing the dynamic range of the °C1 recording system.

In the recording/reproducing system using the monolithic integrated circuit described above, the winding 23a of the rotary transformer 23 is
One end is a recording signal input terminal and a reproduction signal output terminal,
The other end is connected to a power source and is grounded in an alternating current manner. According to this method of use, switching transistors such as transistors Q15, Q16, and Q12 are required, and the circuit becomes complicated. Furthermore, the switching transistor QJ5 requires an external bypass capacitor f31, and the number of bins increases when integrated. Further, the final output transistor Q11 of the recording system requires a large element, but its capacitance becomes an input capacitance when viewed from the reproduction system side, and to avoid this, a separate switch circuit is required. In addition, during recording, a trimmer capacitor 9 is used to adjust the input resonance frequency on the playback side.
The presence of 2B causes deterioration of recording frequency characteristics.

Generally, in a recording/reproducing circuit using a constant current recording type V'l'Ri, it is necessary that the wave number characteristics of the recording current layer in the magnetic head be sufficiently wide. For this purpose, it is necessary that the capacity viewed from the recording quadrant 2 register side to the head side be small, but the presence of the trimmer capacitor is contrary to this. Regarding the playback system,
The head inductance and preamplifier input capacitance form a resonant circuit, which is set to a certain resonant frequency. Therefore, it is a necessary condition that the input capacitance can be set to a certain appropriate value, and the trimmer capacitor cannot be omitted. In this way, in the system described in item 1, the recording and reproducing systems have mutually unfavorable conditions that are combined and conflict with each other.

[Purpose of the invention]

This invention has been made in view of the above circumstances, and allows easy acquisition of frequency characteristics during recording and resonance characteristics during playback, and provides a circuit configuration that is simple to integrate into a monolithic circuit. An object of the present invention is to provide a recording/reproducing circuit that can switch between two recording and reproducing modes.

[Summary of the invention]

According to the present invention, transistor Q21. The output terminal of Q22 is connected to one end of a winding 32a of a rotary transformer, and the other end of the winding 32a is connected to a preregenerative amplifier formed by transistors Q2s and Q24, and to the cathode of a diode 38 (switching element). During playback, the diode 38 is turned on so that the recording bias current flows through the transistors Q22 and Q25 on the output stage side of the current mirror circuit.This simplifies the switching configuration and makes it easy to set the characteristics. It was designed so that it could be obtained.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, numeral 3 is a recording signal input terminal, which is connected to the collector of the transistor Q21. The base and collector of the transistor Q21 are connected, and the emitter is grounded.The transistor Q21 and the transistor Q22 constitute a current mirror circuit. The emitter of transistor Q22 is grounded, and the collector is connected to one end of winding 32a of rotary transformer 32.

A winding 32b of the rotary transformer 32 is connected to a rotating magnetic head 33.

The other end of the winding 32a is connected to the cathode of a diode 38 and to the base of a transistor Q23 via a coupling capacitor 34. This transistor. The base of 23 is grounded via a trimmer capacitor 935 for adjusting the resonance frequency. transistor. 2
The emitter of 3 is grounded and the collector is transistor Q2.
Connected to the emitter of 4. Transistor Q23. Q2
4. The capacitor 34 and the like constitute a regenerative preamplifier. transistor. The collector of 24 is connected to the power supply line 3F l':: through a resistor 36, and the base is connected to a constant voltage bias power supply 38. The reproduction output is derived from the terminal of resistor 36.

One embodiment of the present invention is constructed as described above, and during recording, a recording bias current is supplied from the terminal 3g connected to the anode side of the diode 38. This recording bias current is supplied as a bias current to the recording output transistor Q22 through the winding -32a of the transformer 32.

Next, during reproduction, the diode 38 is in a zero bias or reverse bias state and is turned off. Further, the transistor Q22 is turned on by being supplied with an appropriate DC bias current from the terminal 3, thereby grounding one end of the winding 32a. The pickup output from the rotating magnetic head 33 is then transferred to the rotary transformer 32. Condan f
34 to the base of the transistor Q23,
The signal is amplified and derived from the terminal of the resistor 36. That is, during reproduction, transistor Q22 operates as a switching transistor. According to the circuit of the present invention described above, during the recording operation, the collector of the transistor Q22 and one end of the winding 32a are directly connected, and a capacitor is not connected as in the conventional case. Therefore, there is no influence depending on the capacity of the reproduction side circuit, and there is no deterioration of frequency characteristics as in the conventional case.

Furthermore, during the reproducing operation, the transistor Q22 is
Since it is shared as a switch and a constant current output transistor, there is no need for a bypass capacitor as seen in conventional circuits, and the changeover switch structure becomes simple.

FIG. 4 shows another embodiment of the present invention, a transistor Q
A reproducing switch transistor Q25 is separately connected in parallel with 22, and is turned on by a high level signal from its pace terminal 41 during reproducing operation, grounding one end of winding 32a, and turned off during recording.

Since the current amplification channel width circuit element scale of the recording output stage becomes large, the transistor Q;ll
, balance resistor 4. on the emitter side of Q22. ? , 4J may be required. In such a case, if the output transistor Q22 is also used as a regeneration switch, a balance resistor is connected in series with the regeneration signal system, which may generate thermal noise and cause a reduction in 8N of the regeneration signal system. In such a case, the problem can be solved by setting the transistor Q25 as a dedicated switch.

However, as mentioned above, the dedicated switch transistor Q2
Providing B increases the capacity when viewed as a recording circuit. This suppresses the increase in capacity due to the regeneration switch.
In order to minimize the element scale of the knob regeneration switch and obtain a sufficiently low conduction impedance, as shown in the fifth factor, the regeneration power supply line 37 and transistors Q22゜Q25
By connecting a resistor 42 between the collectors of and flowing an appropriate current, p can be achieved.

〔Effect of the invention〕

As mentioned above, this invention (2) is effective when converting the recording/reproducing and switching circuits of a VTR into a low-voltage monolithic integrated circuit, prevents deterioration of frequency characteristics during recording, and is necessary during playback. It is possible to easily obtain a resonant frequency characteristic without being affected by the recording circuit side, and furthermore, it is possible to provide a recording/reproducing circuit with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional recording/reproducing circuit, FIG. 2 also shows a conventional recording/reproducing circuit, FIG. 3 is a circuit diagram showing an embodiment of the present invention, FIG. 5 are circuit diagrams showing other embodiments of the present invention. Q21 to Q25...transistor, 32...rotary transformer, 38...diode.

Claims (3)

[Claims] (1) A current mirror circuit in which a recording signal input terminal is set as an input terminal and an output terminal is connected to one terminal of the winding of a rotary transformer. An anode is connected to the other terminal of the winding, and a recording bias current input terminal for turning on transistor means on the output stage side of the current mirror circuit during a recording operation is set to the recording bias current input terminal, which is turned off during a reproducing operation. With Motoko. A recording/reproducing circuit comprising a reproducing preamplifier also connected to the other terminal of the winding via a coupling capacitor. (2) The recording/reproducing circuit according to claim 1, wherein the transistor means on the output stage side of the current mirror circuit is only a signal output transistor of the current mirror circuit. (3) The recording/reproducing circuit according to claim 1, wherein the transistor means on the output stage side of the current mirror circuit is a switching transistor connected in parallel to the signal output transistor of the current mirror circuit. 0