JPS58177012A - Fm modulator - Google Patents

Abstract

PURPOSE:To stop the oscillation without deterioration of performance, by taking a base voltage of a transistor (TR) for voltage clip of an astable multivibrator to a power supply voltage at non-operation, at the reproduction except the recording mode. CONSTITUTION:The base voltage of voltage clip TRs Q1, Q2 is switched at a control signal with a switching circuit 8. Contacts of the circuit 8 are selected to the position A to which a bias power supply 9 is connected at the recording mode operating an FM modulator. The contacts are selected to the B position where a power supply Vcc is connected at the modes except the recording mode, at least the reproduction mode. A voltage suitable for the oscillation of the astable multivibrator 3 is given to the voltage V1 of the bias power supply 9, then the accurate oscillation is obtained at the recording mode and a video signal is FM-modulated. Further, at the modes except the recording mode, since the base voltage of the TRs Q1, Q2 is the power supply voltage, normal oscillation is not desired. Since the increase in the stray capacitance giving adverse effects on the normal oscillation is not caused, the performance is not deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM modulator for a magnetic recording/reproducing device.

Conventional P'M modulators have the problem that if they are driven by a power supply that constantly supplies voltage, the FM modulator will oscillate even in playback mode, and the signal will leak into the playback circuit, causing moiré. there were.

A magnetic recording and reproducing device has recording and reproducing modes, and is equipped with a dedicated power supply that supplies voltage in each mode to drive circuits corresponding to these modes (hereinafter referred to as single t/t).
They are called CREC power supply and FB power supply. ). Furthermore, a power source that constantly supplies voltage is also required (hereinafter simply referred to as an AL power source).

).

These power supplies require relatively large amounts of power, making their circuits expensive. In order to reduce the cost of power supply circuits, it is necessary to unify the power supply. For this method, the only power source that constantly supplies voltage (AL power source) is used.

The best method is to turn on and off the circuits that operate in recording and playback modes using control signals. However, in this case, the conventional FM modulator has a problem in that it is difficult to stop oscillation during reproduction.

FIG. 1 shows a conventional FM converter and one problem will be explained. This is an integrated emitter-coupled unstable multivibrator. 1 is an input terminal.

2 is a voltage/current conversion transistor, 3 is an unstable multivibrator, 4 is an excavated capacitor, 5 is an oscillation frequency adjustment circuit, 6 is a limiter, and 7 is an output terminal. a, b, c
, d indicate the terminals of the IC. A video signal is supplied to an input terminal 1, and a voltage/current conversion transistor 2 converts this signal into a change in current, which is converted into a change in frequency by an astable multivibrator 6, and is FM modulated.

The amplitude of this signal is limited by the limiter 6, and the FM signal is sent to the output terminal 7.
A modulated signal is obtained.

The oscillation frequency adjustment circuit 5 is an unstable multivibrator 5.
This is to match the 0 excavation frequency to a predetermined standard value. (For example, in the VH5 standard, the sync chip station wave number MEz, white peak frequency 4.
It is 4MEz. ) The current flowing through the capacitor is adjusted by changing the surrounding variable resistors VR1 and VB2.

The oscillation frequency of the astable multivibrator 3 is.

The current, C is the capacitance of the oscillation capacitor, and VO is the excavation voltage, that is, the voltage clipping transistor Q1. There is a voltage between the base of Q2 and the power supply Vcc, and since this formula and circuit operation are well known, their explanation will be omitted.

The FM modulator is necessary only in the recording mode, and oscillation during reproduction is undesirable as described above.

When the power supply Vcc is driven by the REt' power supply, no excavation occurs during reproduction, but when the power supply Vcc is driven by the AL power supply, it excavates also during reproduction.

Even if the base voltage of the voltage/current conversion transistor 20 is grounded and turned off, even if the constant current source of transistors Q15 to (718) is turned off, the activation frequency adjustment circuit 5 around the IC
It oscillates due to the current from the 1 as shown in the figure
There is also a method of connecting the diode D1 to -1 of the excavation capacitor 4 and applying a high voltage during playback to forcibly turn off the operation, but this increases the number of components by one and the parallel capacitance C5 of the diode D1 causes the waveform to rise. is asymmetrical (there is a problem that second-order distortion increases).

The present invention eliminates the drawbacks of the prior art described above.

To provide an FM modulator that can easily stop excavation when not in use without increasing the number of peripheral parts or deteriorating performance.

The feature of the present invention is that the base voltage of the transistor for voltage clipping of the astable multi-noise ibrator is fixed.

One oscillation is stopped by using a sufficiently high voltage (for example, power supply voltage) when not in use.

An embodiment of the FM modulator of the present invention will be explained with reference to FIG. 1 is an input terminal, 2 is a voltage/current conversion transistor, 3
is an unstable multivibrator, 4 is an oscillation capacitor, and 5 is an oscillation capacitor.
is an oscillation frequency adjustment circuit, 6 is a limiter, 7 is an output terminal,
8 is a switching circuit, 9 is a bias power supply, and 10 is a control signal input terminal. Components that are the same as those in the prior art are given the same reference numerals. A video signal is supplied to input terminal 1.

This signal is converted into a change in current by a voltage/current conversion transistor 2, which is converted into a change in frequency by an unstable multi-noise (ibrator 6) and FM modulated.The limiter 6 limits the amplitude of this signal.

An FM modulated signal is obtained at the output terminal 7. The oscillation frequency adjustment circuit 5 is for adjusting the oscillation frequency of the unstable multivibrator 5 to a specified value. Power supply Vcc is AL
It is driven by a t source.

This embodiment differs from the conventional example in that the voltage clip transistor Q1. (/2 base voltage is switched by a control signal. 8 is a switching circuit for this purpose. The contacts of the switching circuit 8 are used in the recording mode to operate the FM modulator.

It is connected to the A side to which the bias power supply 9 is connected. And at least in playback mode other than recording mode, the power supply V
CC is connected B@IIC is connected. This switching operation is performed by a control signal supplied to the control signal input terminal 10.

The voltage limit 1 of the bias power supply 9 is given a voltage suitable for the oscillation of the unstable multivibrator 5, as in the past, so normal oscillation is obtained in the recording mode as before, and the video signal is FM modulated. . On the other hand, in modes other than recording mode, the voltage clipping transistor (/1 j Q2
Since the 0 base (0 point) voltage becomes the power supply voltage, normal oscillation cannot be expected. The diode-connected transistor Q5 is.

Transistor Q' e Q20 base-emitter voltage (
Vag) for temperature compensation, but as described above.

In other than recording mode, transistor Q1. Since the base voltage of transistor Q2 is the same as the base voltage of transistor Q5, transistor Q1. Even if Q2 is turned on, transistor Q
1, the resistor (R1, R
No voltage drop occurs in 2). Therefore, since there is no potential difference between the emitter of the transistor Q1 and the emitter of the transistor Q2, the unstable multi-biple pretaro does not oscillate. Even if there is variation between the elements of transistors Q1 to Q3 and a potential difference occurs, the transistor Q's
Since the voltage does not turn Q5 on and off, oscillation does not occur. This is because the present invention switches the base voltage of the voltage clipping transistor.

There is no increase in stray capacitance that would adversely affect normal mK generation. Therefore, performance does not deteriorate.

FIG. 3 shows an embodiment of the embodiment shown in FIG.

Resistors Rs, Ra, R5 and transistor Q6 are
It constitutes a switching circuit 8 and a bias power supply 9.

In the recording mode, a high voltage is applied to the control signal input terminal 10 and is applied to the base of the transistor Q6 via the resistor R5, so that the transistor Q6 is saturated. Since the collector-emitter saturation voltage of transistor Q6 is sufficiently smaller than the power supply voltage, the voltage at the 0 point is the voltage obtained by dividing the power supply voltage by resistors R6 and R4. This voltage is V
The values of the resistors Rs and R4 are selected so that 1.

Therefore, normal FM modulation is performed. - 10,000, except in the recording mode where no voltage is applied to the control signal input terminal 10.
Since the transistor Q6 is turned off, the voltage at the 0 point becomes the power supply voltage, and excavation stops. In this embodiment, oscillation can be stopped using a very simple circuit with a very small number of parts.

FIG. 4 shows another embodiment of the embodiment shown in FIG. In this embodiment, a signal from the control signal input terminal 10 is used to turn off the transistors Q15 to Q418, which serve as constant current sources, except in the recording mode. This is because the signal input to the control signal input terminal 10 is used as a bias for the constant current source.

A relatively stable high voltage is supplied in the recording mode. In modes other than recording mode, this terminal is at ground potential. In order to obtain such a control signal, it is best to switch the voltage from, for example, a Zener power source. When a high voltage is supplied to the control signal input terminal 10 in the recording mode, the emitter of the transistor Q24 becomes high potential and the constant current source transistors Q15 to Q1B are turned on. Since the transistor Q21 is also turned on, a current determined by the emitter voltage and the resistor R10 flows from the power supply through the resistor RN to the collector KR. The collector of the transistor Q21 is connected to the transistor Q21.
Since the base (0 point) of mQ2 is connected to K, this voltage becomes VlfC.

If designed in this way, normal FM modulation will be performed in recording mode. On the other hand, when the control signal input terminal 10 is at ground potential other than in the recording mode, the constant current source transistor (, 115
~Q18 is turned off, and transistor Q21 is also turned off. Therefore, the potential at point ■ becomes the power supply voltage, and one oscillation does not occur.

This example is.

Although it has a somewhat large number of parts, it has the advantage of reducing current consumption in unnecessary modes other than recording mode. In addition, IC
An increase in the number of internal parts results in a much smaller cost increase than in the case of one peripheral circuit.

In the above explanation, in addition to the recording mode, the base voltage of the voltage clipping transistor is set to the power supply voltage, but if the unstable multivibrator 3 is operating at a voltage lower than the power supply voltage 1'cc, There is no need to do this, and it is sufficient to set the voltage high enough to stop the six oscillations.

Also, the oscillation can be stopped in all modes other than the metering mode, but only in the regeneration mode, where negative effects are likely to occur.

Original F! According to AK, in an FM modulator that is constantly supplied with voltage, oscillation can be easily stopped to a mode that is not needed, so there is almost no cost increase (and there is no performance deterioration. Since it becomes possible to unify the power supply circuit, it also has the effect of reducing the cost of the power supply circuit.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional FM modulator, Fig. 2 is a circuit diagram of an embodiment of an FM modulator according to the present invention, and Fig. 3 is a circuit diagram of an embodiment embodying Fig. 2. FIG. 4 is a circuit diagram of another embodiment that embodies FIG. 2. 3... Unstable multivibrator, 4... Oscillation capacitor, 5... Oscillation frequency adjustment circuit, 8... Switching circuit, 9... Bias power supply, 10... Control signal input terminal. Sai 1 Illustration, t 2 Illustration 3 Illustration 4 Illustration

Claims (1)

[Claims] A magnetic recording/reproducing device having at least a recording mode and a reproduction mode, which includes an unstable multivibrator driven by a power supply to which voltage is constantly supplied, and an oscillation frequency connected to an oscillation capacitor of the unstable multivibrator. with adjustment circuit. The switching circuit includes a switching circuit that switches the base voltage of a voltage clipping transistor of the unstable multivibrator, and is configured to switch the base voltage of the clipping transistor so as to stop the oscillation of the unstable multivibrator in at least a playback mode other than a recording mode. Characteristic F
M modulator.