JPS5857658A - Reproducing circuit of control signal - Google Patents

Abstract

PURPOSE:To obtain a reproducing circuit of control signals which contains an inverting circuit with a large dynamic range and with no distortion of signal, by obtaining an adverse phase output from the output of an amplifier via a current mirror circuit. CONSTITUTION:A current mirror circuit is provided with transistors TR14 and TR17 plus resistances 15 and 16. The collector current of the TR14 is decided by the difference between the base-emitter voltage VBE of the TR14 and the voltage VD of the output D of an amplifier 1. This current value is transmitted to the collector current of the TR17 with a current transmitting ratio which is decided by the resistances 15 and 16. Here a signal E having the phase adverse to the output D of the amplifier 1 is obtained at a joint of collectors of the resistances 16 and 17. The signal E is converted into a signal E' having the same phase as the signal E via a TR18 which forms a level shifting circuit. Either the signal E' or the output D is extracted to a switch circuit 12 in response to the forward or backward reproduction mode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing apparatus (VTR) having a reverse reproduction function.
) relates to a control signal reproducing circuit.

In general, in a VTR with a reverse playback function, during reverse playback, the polarity of the control signal taken out by the control head is reversed compared to during normal playback, so during reverse playback, the polarity of the control signal taken out by the control head is reversed compared to the control signal during forward playback. In order to obtain control signals with the same phase, the control signals are regenerated through an inversion circuit.

FIG. 1 shows a conventional control signal reproducing circuit having an inversion circuit. In FIG. 1, a signal (A) taken out by the control head is applied to an amplifier (1),
The output of this amplifier (1) is a constant current circuit (2).

Reference voltage source (3), T-transistor (4) <5>
(6) (7) and resistors (8), (9), and is input to a differential amplifier composed of QO (II). The positive phase output (B) and negative phase output (0) of this differential amplifier are respectively connected to the input of a switch circuit (A). The operation of the circuit shown in Figure 1 is such that the signal amplified by the amplifier (1) is input to the differential amplifier, and the positive phase output (B) or the negative phase output (
Either one of C) is taken out by the switch circuit 04 depending on whether the normal rotation regeneration or the reverse rotation regeneration is performed. That is,
Even if the polarity of the signal taken out by the control head during reverse playback is reversed compared to during normal playback,
The reproduced control signal can have the same phase regardless of forward rotation reproduction or reverse rotation reproduction.

Here, the signal level of the control signal reproduced by the conventional circuit shown in FIG. 1 will be explained. Since the input section of the differential amplifier has a two-stage Darlington configuration with transistors (4) and (5), the dynamic range of the positive phase output rises to 0 when the voltage of the reference voltage source (3) is Va.
Then, Va, + 2VBK -Vcz(sat)'
(1) becomes. Here, VBE is the voltage between the base and emitter of the transistor, and VCE (sat) is the saturation voltage between the collector and emitter of the transistor. If the lowest potential of the input signal is VL, the dynamic range of the negative phase output (0) is VL +2VBE -VcE(eat)
(2) becomes.

Here, the dynamic range can be increased by increasing the number of Turlington connection stages of transistors in the input section of the differential amplifier, but since it is limited to the voltage of the DC voltage source, the Turlington connection The number of connection stages is limited.

That is, in the conventional control signal reproducing circuit, the dynamic range of the negative phase output is small. Also, when this circuit is integrated into a semiconductor circuit, the amplification degree of the differential amplifier,
Due to variations in the current value of the constant current circuit and resistances (8), (9), etc., the reproduced signal may become larger than the dynamic range of the negative phase output of the differential amplifier, and in this case, the negative phase output signal produces distortion that follows and inverts the input signal, and due to the distortion of the control signal, malfunctions may occur during reverse playback of the VTR.

The present invention solves the above conventional problems and provides a control signal reproducing circuit having a large dynamic range and an inverting circuit without signal distortion.

An embodiment of the present invention will be described below with reference to FIG. The signal (A) extracted by the control head is applied to an amplifier (1), the output (D) of which is the output of a transistor whose emitter is grounded and whose base and collector are shorted. The collector is connected to the resistor (IQ).The base-collector connection point of the transistor 0 is the base of the transistor α whose emitter is grounded and whose collector is connected to the DC voltage source a3 through the resistor αQ. The connection point between the collector of the transistor (171) and the resistor αQ is connected to the base of the transistor a whose collector is connected to the DC voltage source α.

The emitters of the amplifier (1) and the transistor Q barrel are each connected to the input of the switch circuit Tsukuda.

Next, the operation of the circuit having the configuration shown in FIG. 2 will be explained.

Transistor 04) αη and resistor 0f9Q (9 constitute a current mirror circuit), and the output of amplifier (1) (
The collector current of the transistor α4) is determined by the voltage difference between the voltage VD of the transistor D) and the base-emitter voltage VBE of the transistor α4). This current value is transmitted to the collector current of the transistor 07) at a current transfer ratio determined by the resistor 0Q. Therefore, at the connection point between the resistor QQ and the collector of the transistor 0η, the output (D) of the amplifier (1) is converted into a signal (B) having the same phase. Either this signal (Iff) or the output (D) of the amplifier (1) is taken out to the switch circuit 04 depending on the forward rotation reproduction or the reverse rotation reproduction. In other words, during reverse playback, the polarity of the signal taken out by the control head is different from that during forward playback.
Even if it is reversed, the reproduced control signal can have the same phase regardless of whether the reproduction is normal or reverse.

Next, the signal level of the control signal reproduced by the circuit according to the embodiment of the present invention shown in FIG. 2 will be explained. The dynamic range of the output (D) of the amplifier (1) is determined by the circuit of the amplifier (1), and ideally it will be the power supply voltage Vcc, and the signal (E) in reverse phase with the output (D) will be Vcc - It becomes VOE (eat). Also, the signal will not be distorted.

DC voltage VD of the output (D) of the amplifier (1)
O is chosen to be 1/2 of the power supply voltage. Here VDC='H
vcc and the resistance value of the resistor α4)Ql is the same,
Signal (hi) of the emitter terminal of the transistor DIIO
In this case, the same DC voltage as the output (D) of the amplification 'a(1) is obtained, the amplification degree is 1, and a signal with only the phase inverted can be obtained.

As described above, in the control signal regeneration circuit of the present invention, an anti-phase output is obtained from the output of the amplifier via the current mirror circuit, so the dynamic range of the anti-phase output is determined by the amplifier circuit to which the control signal is input. Regardless of positive phase output or negative phase output, it can be configured into a circuit with a large dynamic range and no signal distortion.
In R, a stable image can be obtained during reverse playback as well as forward playback.

[Brief explanation of the drawing]

Figure 1 is an example of a conventional control signal regeneration circuit.
FIG. 2 is a block diagram showing an embodiment of the control signal reproducing circuit of the present invention. (1)...Amplifier, 0s...Switch circuit, θ→・
...DC voltage register agent Yoshihiro Morimoto

Claims (1)

[Claims] 1. In a magnetic recording and reproducing device that has forward playback and reverse playback functions, a control signal taken out by a control head is amplified by an amplifier, and the output of this amplifier is a A second transistor whose emitter is grounded and whose collector is connected to a DC voltage source via a second resistor is connected to the base-collector connection point of the first transistor through a first resistor. A control signal regeneration circuit connected to a base of a transistor and selectively outputting a signal at a connection point between the collector of the second transistor and a second resistor and an output signal of the amplifier. .