JPS5822259Y2 - Negative feedback amplifier circuit for magnetic recording and reproducing equipment - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a negative feedback amplifier circuit for a magnetic recording/reproducing device such as a video tape recorder, and is an improvement of the switching circuit for recording and reproducing.

A video tape recorder is usually provided with a recording function for recording on a magnetic tape and a reproduction function for reproducing signals from the magnetic tape.

In such magnetic recording and reproducing apparatuses, in order to reduce the number of circuits such as amplifiers, attempts have been made to form amplifiers used during recording and reproduction into one circuit.

However, due to the recording characteristics and conditions of magnetic tape, when using one amplifier, it is inconvenient if this amplifier is used for both recording and reproduction simultaneously.

Therefore, conventionally, a recording/reproduction switching circuit as shown in FIG. 1 has been used.

1 is an amplifier, and this amplifier 11 is provided with a first switch 12 for level switching and a second switch 13 for switching a feedback line.

The first switch 12 leads the output of the amplifier 11 directly or through the variable resistor 14 to the output terminal 15, and is switched to the fixed contact Pl side during recording and to the fixed contact Pl side during playback.

The second switch 13 is switched to a fixed contact R2 on the recording negative feedback element 16 side during recording, and switched to a fixed contact P2 on the reproduction negative feedback element 17 side during playback.
The frequency characteristics of the amplifier 11 during recording and playback can be switched.

As described above, since the conventional circuit is a recording/reproduction switching circuit having two switch sections, it has drawbacks such as a complicated configuration when the number of parts increases and switching noise generated during switching.

The present invention has been made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a recording/reproduction switching circuit which can reduce the number of switch sections to 2i and switch the amplifier characteristics at a low cost.

Embodiments of this invention will be described in detail below with reference to the drawings.

That is, the amplifier 22 shown in FIG. 2, to which the video signal for recording or reproduction is applied from the input terminal 21, has its output terminal 23 connected to one terminal of the first negative feedback circuit 24, and also has a variable It is connected to one terminal of the resistor 25.

The negative feedback circuit 24 is a circuit in which a resistor 27 is connected in parallel to a series circuit of a resistor 28 and a capacitor 26, and the other terminal is negatively fed back to the control terminal of the amplifier 22.

Furthermore, a first fixed contact Ro of a recording/reproducing changeover switch SW is connected to a connection point between the capacitor 26 and the resistor 25 of the negative feedback circuit 24.

The movable contact X of this changeover switch SW is grounded, and the second fixed contact PO is connected to the other terminal of the variable resistor 25.

Further, the other terminal of the variable resistor 25 is connected to the control terminal of the amplifier 22 via a resistor 29 and grounded via a resistor 30.

The slider 251 of the variable resistor 25 derives the output of the entire circuit and is connected to the output terminal 31.

The first embodiment of the recording/reproducing switching circuit of the present invention is constructed as described above. During recording, the movable contact X of the changeover switch SW is switched to the fixed contact Ro side, and during playback, the fixed contact PO
can be switched to the side.

First, when the movable contact Sets the high frequency falling type frequency characteristics for the output.

Further, in this case, since one end of the variable resistor 25 is grounded, the output level of the amplifier 22 can be varied from zero to one by moving the slider.

Next, when the movable contact X is switched to the fixed contact Ro side and set to the recording state, the signal input to the input terminal 21 is amplified by the amplifier 22, and its output is sent to the variable resistor 25 and the negative feedback element for recording. The signal is fed back to the negative feedback input of the amplifier 22 via a resistor 29 as a main component.

Further, since the reproducing negative feedback circuit 24 is grounded midway, it does not function as a negative feedback element, and the circuit as a whole has a flat frequency characteristic.

However, the impedance of the capacitor 26 of the regenerative negative feedback circuit 24 is made sufficiently larger than the resistor 30 that functions as a feedback attenuation resistor.

Furthermore, one end of the variable resistor 25 is a negative feedback resistor 29 for recording.
Since it is fed back to the negative feedback input via the variable resistor 25
If the resistance value of the resistor 29 is made sufficiently larger than the total resistance value of the resistor 29, an output signal having approximately the same magnitude as the output of the amplifier 22 will be obtained at the output terminal 31 without significantly affecting the position of the slider 251 of the variable resistor 25. I can give it.

Although the above embodiments have been exemplified by mechanical switches, the present invention can easily be replaced with electronic changeover switches as shown in FIG. 3, and switching noise is less likely to affect the switch.

That is, the same parts as in FIG. 2 are denoted by the same reference numerals, and the explanation thereof will be omitted to describe the structure. Reference numerals 32 and 33 are switching transistors.

The collector of the switching transistor 32 is connected to the connection point between the capacitor 26 and the resistor 25, and the terminal is grounded.

The collector of the switching transistor 33 is connected to the connection point between the resistor 29 and the variable resistor 25, and the emitter is grounded.

The switching transistors 32 and 33 are
A signal at a level that turns on the base when necessary is applied to each base, and the switching transistor 33 is turned on during reproduction, and the switching transistor 32 is turned on during recording.

Note that the above-mentioned transistor can be used as one switching circuit element, and the control signal can be easily obtained from the recording/reproducing changeover switch.

As described above, the present invention can provide a negative feedback amplifier circuit for a magnetic recording/reproducing device in which the switch section is simplified and the amplifier characteristics can be easily changed at a low cost.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the negative feedback amplifier circuit of a conventional magnetic recording/reproducing apparatus, FIG. 2 is a circuit diagram showing an embodiment of the negative feedback amplifier circuit of the magnetic recording/reproducing apparatus of the present invention, and FIG. 3 is a circuit diagram of another embodiment of the present invention. FIG. 3 is a circuit diagram showing an example. 21... Input terminal, 22... Amplifier, 24... Regenerative negative feedback circuit, 25... Variable resistor, 26... Capacitor, 2γ, 28, 29. 30... Resistor.

Claims (1)

[Scope of utility model registration request] A regenerative negative feedback circuit element formed by connecting a resistor in parallel to a series circuit of a capacitor and a resistor, an amplifier to which this regenerative negative feedback circuit element is connected to its input/output terminal, and a circuit connected between the input terminal of this amplifier and ground. , a resistor having an impedance lower than that of the capacitor of the regenerative negative feedback circuit element, a variable resistor having one end connected to the output side of the amplifier and having an output terminal for taking out the output of the amplifier, and other components of the variable resistor. A resistor having one end connected to one end and the other end connected to the input side of the amplifier and having a resistance value sufficiently larger than that of the variable resistor, and a connection point between this resistor and the variable resistor, and a connecting point between the resistor and the variable resistor, 1. A negative feedback amplifier circuit for a magnetic recording/reproducing device, comprising switch means for alternately switching and grounding a connection point between a capacitor and a resistor during reproduction and writing, respectively.