JPH05199496A - Mode detecting circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To enable the integration of the entire mode detection circuit. [Structure] The phase of the reproduced FM input signal is shifted by the phase shifter 20 using a gm amplifier, and the phase-shifted signal and the original reproduced FM input signal are balanced-modulated by the balanced modulator 21 to obtain the difference between them. A signal is output, the difference signal is smoothed by the smoothing circuit (22), and the smoothed signal and the reference voltage V are compared by the comparator 23.
By comparing with, the mode is determined and the mode detection signal is output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mode detection circuit for detecting a recording mode (high band, normal) such as VTR.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional mode detection circuit.

In FIG. 3, (1) is a peaking amplifier,
(2) is an LC resonance circuit using the coil (3) and capacitors (4) and (5), (6) is an amplifier, (7) is a smoothing circuit, and (8) is a comparator. The amplitude of the reproduced FM input signal is detected by the resonance circuit (2) and the peaking amplifier (1), this amplitude signal is amplified by the amplifier (6), then smoothed by the smoothing circuit (7), and the comparator (8 ) And compared with a predetermined reference voltage V, the mode is discriminated and a detection signal is obtained.

FIG. 4 shows another example of the conventional mode detection circuit.

In FIG. 4, (10) is a phase shift circuit, (11) is an LC resonance circuit using a coil (12) and capacitors (13) and (14),
(15) is a balanced modulator, (16) is a smoothing circuit, and (17) is a comparator. The phase of the reproduction FM input signal is shifted by the resonance circuit (11) and the phase shift circuit (10), and the signal whose phase is shifted and the original reproduction FM input signal are balanced-modulated by the balanced modulator (15). A difference signal is obtained. Then, from this difference signal, as in the case of FIG. 2, the smoothing circuit (16) and the comparator
The detection signal is obtained by (17).

[0006]

In any of the above mode detection circuits, the coil (3) (1
The LC resonant circuits (2) and (11) including 2) are externally attached, and it is impossible to integrate the entire circuit.

The object of the present invention is to solve the above problems,
An object of the present invention is to provide a mode detection circuit capable of integrating the entire circuit.

[0008]

A mode detection circuit according to the present invention is characterized by including a phase shifter using a gm amplifier (an amplifier using the transconductance gm of a differential amplifier as a parameter). It is a thing.

[0009]

The phase shifter using the gm amplifier shifts the phase of the reproduced FM input signal, and the detected output is obtained from the phase-shifted signal and the original reproduced FM input signal as described above. Since the phase shifter uses the gm amplifier, it is not necessary to use the coil, and therefore the whole circuit can be integrated.

[0010]

Embodiments of the present invention will be described below with reference to FIGS.

In FIG. 1, (20) is a phase shifter (active filter) using a gm amplifier, (21) is a balanced modulator, and (2)
2) is a smoothing circuit, and (23) is a comparator.

In the above mode detection circuit, the reproduction FM
The input signal is input to the phase shifter (20), its phase is shifted, and output to the balanced modulator (21). In the balanced modulator (21),
The phase-shifted signal which is the output signal of the phase shifter (20) and the original reproduction FM input signal are balanced-modulated and a difference signal between them is output. This difference signal is smoothed by the smoothing circuit (22) to become a DC voltage signal and sent to the comparator (23). Comparator (2
In 3), the DC voltage corresponding to the difference signal and the predetermined reference voltage V
The mode is determined by comparing and, and the detection signal is obtained from the result.

An example of a phase shifter using a gm amplifier is shown in FIG.

In FIG. 2, (24) is an input terminal, (25) is an output terminal, (26) is a gm amplifier, (27) is an amplifier, (28), (29) and (3).
0) is a resistor and (31) is a capacitor. The configuration of the gm amplifier is well known, and the cutoff frequency can be controlled by changing the mutual conductance gm of the differential amplifier that constitutes the gm amplifier. The phase shifter (20) of the mode detection circuit of FIG. 1 is, for example, the one in which the phase shifter of FIG. 2 is connected in two stages.

[0015]

As described above, according to the mode detecting circuit of the present invention, since the phase shifter using the gm amplifier is provided, the whole circuit can be integrated.

[Brief description of drawings]

FIG. 1 is an electrical block diagram of a mode detection circuit showing an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing an example of a phase shifter using a gm amplifier.

FIG. 3 is an electric circuit diagram showing an example of a conventional mode detection circuit.

FIG. 4 is an electric circuit diagram showing another example of a conventional mode detection circuit.

[Explanation of symbols]

 (20) Phase shifter using gm amplifier (21) Balanced modulator (22) Smoothing circuit (23) Comparator (26) gm amplifier

Claims (1)

[Claims] 1. A mode detection circuit including a phase shifter using a gm amplifier.