JPH0260309A - Recording amplifier for digital signal - Google Patents

Abstract

PURPOSE:To prevent the saturation of the TR of an amplifying step by including an amplifying transistor(TR) of an input signal, a current source to supply a power source to the TR and an element to feed back the output of the current source to the control terminal. CONSTITUTION:The output of a current source is fed back through a resistance Rf for feedback as a feedback element to the base of TR4. The resistance Rf for feedback is connected between the base collectors of the TR4, and thus, an input signal level is raised. The potential difference between the base and the emitter of a TR4 exceeds 0.7V, and even then, the collector potential of the TR1 is lowered, and communicated through the resistance Rf to the base of the TR4. For such a reason, it is sufficient that the base potential of the TR4 is lowered, as the result, the internal resistance of the current source is lowered and the collector potential of the TR1 is reduced 2-3V lower than supply voltage Vcc. For this reason, the input signal level can be increased more and the recording current of a head H can be made into >=2 times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in Industry-1-] The present invention relates to a magnetic recording/reproducing device, and particularly to a recording amplifier for digital signals.

[Conventional technology]

Conventionally, this type of digital signal recording amplifier has a transistor that receives and amplifies an input signal, and a current source that supplies power to the transistor, and the input signal is only amplified by the transistor. In reality, the current source is not controlled.

[Problem to be solved by the invention]

Conventionally, the control signal is not fed back to the control terminal of the current source, so if the input signal level of transistor 1 to transistor in the amplifier stage exceeds the forward level between the base and emitter, the transistor in the amplifier stage will become saturated. However, the disadvantage was that the amplification effect was lost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital signal recording amplifier that solves the above problems.

[Means to solve the problem]

In order to achieve the above object, the digital signal recording amplifier according to the present invention includes a transistor that receives and amplifies an input signal, a current source that supplies power to the transistor, and a current source that outputs the output of the current source. and an element that feeds back to the control terminal.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

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

In the figure, TRI and TR2 are amplification transistors that amplify input signals, R1, R2, and R3 are bias resistors, and Dl is a bias diode. VRI is a variable resistor for balance adjustment, T is a high frequency transformer, and H is a head. TR4 is a current source transistor constituting a current source, TR3 is a control transistor that receives a control signal to transistor TR4, and R2 is a feedback resistor.

Digital input signals whose phases are inverted to each other are input to the input terminals INI and TN2, and the transistors TRI and TR
After being amplified by step 2, the signal is applied to the head H via a high frequency transformer T.

A control signal for operating a current source composed of a transistor TR4 is added to the control terminal IN3, and due to the action of the transistor TR3, the current source operates at a high level of +5 [■], and at a low level of 0 [V]. The current source stops operating. The output of the current source is applied to the collectors of transistors TR1 and TR2 via a high frequency transformer T.

In addition, the output of the current source is a feedback resistor Rf as a feedback element.
It is fed back to the base of transistor TR4 via.

As shown in FIG. 2, input terminal IN1. ．． Digital signals whose phases are mutually inverted are applied to IN2.

The input signal is positively biased by 0.7 V by a bias circuit including a diode D1 and resistors R1, R2, and R3.

Furthermore, as shown in Figure 3, when a positive direction signal is applied to the transistor TRI, a potential of 0.7 (V) subtracted from the base potential in the same phase appears at the emitter of the transistor TR1, and a negative direction signal appears at the emitter of the transistor TR1. When the signal is applied, it is fixed to 0 (V).

As shown in FIG. 4, without the feedback resistor R2, when the level of the input signal is increased to increase the recording current of the head H, the difference between the base potential and emitter potential of the transistor TRI becomes 0.7. 1 to transistor T when exceeding (V)
RI is saturated and the collector potential of transistor TRI is 0.
Descend to near [■].

Similarly, when the signal is in the negative direction, the transistor TR2 becomes saturated, and as a result, the output potential of the current source decreases, and the current source no longer functions as an amplifier. Therefore, by connecting the feedback resistor Rf between the base and collector of the transistor TR4, the input signal level is increased and the transistor T
Even if the potential difference between the base and emitter of RI exceeds 0.7 (V), the collector potential of transistor TRI decreases.
This is transmitted to the base of the transistor TR4 via the resistor R2, and the base potential of the transistor TR4 decreases. As a result, the internal resistance of the current source decreases, and the collector potential of the transistor TRI becomes the power supply voltage V. 2~ from C
A decrease of only 3 [v] is sufficient. Therefore, the input signal level can be increased more than before, and the recording current of the head H can be more than doubled.

〔Effect of the invention〕

As explained above, the present invention has the effect that the input level of the transistor in the amplification stage can be increased more than the conventional one, and the output current can be increased more than the conventional one.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
Input signal terminal IN1 in the figure. 3 and 4 are diagrams showing input signals of IN2, and FIGS. 3 and 4 are diagrams showing signals at the base and emitter of the transistor TRI in FIG. 1. INI, IN2・Input terminal IN3・Control terminal D
Diodes for bias R1, R2, R3・Resistors for bias TRI, TR2・・Amplification transistor TR3・・Control transistor TR4 Current source transistor ■ Old・・Variable resistor for balance adjustment

Claims (1)

[Claims] (1) A digital signal characterized by including a transistor that receives and amplifies an input signal, a current source that supplies power to the transistor, and an element that feeds back the output of the current source to a control terminal of the current source. recording amplifier.