JP2002033630A - Signal amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal amplifier circuit that can easily and stably amplify a signal subjected to desired band limit in spite of a simple hardware configuration. SOLUTION: An integration circuit consisting of a resistor and a varactor diode whose static capacitance can be varied with an external control voltage is placed in a pre-stage of a signal amplifier circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal amplifying circuit for amplifying an electric signal.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a conventional signal amplifier circuit.

[0003] The transistor 11 is turned on / off by an enable signal from an enable signal input terminal 14. When an ON enable signal is input from the enable signal input terminal 14, an integrating circuit including the resistor 9 and the capacitor 10 is formed, and the analog signal input from the signal input terminal 8 is band-limited. An example of the frequency characteristic of the integrating circuit including the resistor 9 and the capacitor 10 at this time is shown by a characteristic line 31 in FIG. The characteristic line 31 of the integration circuit
Is generally known to be determined by the resistance value and the capacitance value of the resistor 9 and the capacitor 10.

In this way, the resistor 9 and the capacitor 10
The analog signal whose band has been limited by the integrating circuit composed of the following is amplified by the amplifier 12 (AMP: Amplifier) and output from the signal output terminal 13.

Next, when an enable signal for turning off the transistor 11 is input from the enable signal input terminal 14, an integrating circuit constituted by the resistor 9 and the capacitor 10 is not formed. An example of the frequency characteristic of the integrating circuit at that time is shown by a characteristic line 30 in FIG. The analog signal input from the signal input terminal 8 is amplified by the amplifier 12 without band limitation and output from the signal output terminal 13.

[0006]

As described above,
Whether or not to apply the band limitation to the analog signal from the signal input terminal is determined by the enable signal from the enable signal input terminal 14. If it is necessary to apply the band limitation to the analog signal and want to change its frequency characteristic, It is necessary to replace parts of the resistor or the capacitor constituting the integration circuit. Therefore, there is a problem that it is difficult to cope with a case where it is desired to easily and arbitrarily set the frequency characteristic while monitoring the analog signal from the signal output terminal 13.

Further, if the resistance or capacitor constituting the integration circuit is a variable resistor or variable capacitor, the frequency characteristics of the integration circuit can be set arbitrarily and easily. The capacitance value must be set by rotating mechanically. To reproduce frequency characteristics, it is necessary to know the rotation position or rotation angle. Alternatively, there arises a problem that the rotation angle fluctuates and the frequency characteristic of the integration circuit changes accordingly.

An object of the present invention is to solve these problems and to provide a signal amplifier circuit capable of easily changing a stable frequency characteristic with a simple hardware configuration.

[0009]

In order to achieve the above object, the present invention provides an integrating circuit comprising a resistor and a variable-capacitance diode for changing the capacitance by an external control voltage to convert an analog signal into a desired signal. It is arranged before the signal level is amplified.

[0010]

As a result, if the input analog signal is band-limited or if the frequency characteristic is to be changed when the band is limited, it can be easily achieved by varying the control voltage from the outside. Thus, it is possible to realize a signal amplifying circuit having a stable and band-limited frequency characteristic with variable and easy reproducibility.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention is shown in FIG.

1 is a signal input terminal, 2 is a resistor, 3 is a coupling capacitor for cutting a DC component, 5 is a variable capacitance diode, 4 is a control voltage for inputting a control voltage 23 of the variable capacitance diode 5. An input terminal, 6 is an amplifier (AMP), and 7 is a signal output terminal.

Hereinafter, this operation will be described. When an analog signal is input from the signal input terminal 1, the analog signal is band-limited by an integrating circuit including the resistor 2 and the variable capacitance diode 5.

Here, the frequency characteristic of the integrating circuit composed of the resistor 2 and the variable capacitance diode 5 is determined by the resistance value and the capacitance value of the capacitor as described above. The variable capacitance diode 5 is a diode whose capacitance is varied by a control voltage 23 applied from the control voltage input terminal 4. FIG. 4 shows the characteristics of the variable capacitance diode. The control voltage 23 applied as shown in FIG.
2, the capacitance of the variable capacitance diode 5 becomes C1
From C2 to C2.

Therefore, the resistance 2 can be easily changed by changing the control voltage 23 applied to the variable capacitance diode 5.
And the frequency characteristic of the integrating circuit composed of the variable capacitance diode 5 can be changed.

In this manner, the analog signal whose band is limited by the integrating circuit including the resistor 2 and the variable capacitance diode 5 is amplified by the amplifier 6 and output from the signal output terminal 7.

FIG. 5 shows a second embodiment of the present invention. This example is an example applied to a television camera device.

Reference numeral 15 denotes a camera head, which is a solid-state image sensor 16
Analog video signal 22 with (CCD: Charge Coupled Device)
Is obtained. Reference numeral 17 has a configuration and a function similar to those of FIG.
Is a signal amplifying circuit supplied from a CPU 18 (CPU: Central Processing Unit). Signal amplification circuit 17
, And becomes an analog video signal amplified to a desired signal level. This signal is supplied to the A / D converter 19 (A
/ D: Analog to Digital Converter). The digitized video signal is subjected to necessary signal processing in a digital signal processing circuit 20, and a digital video signal is output from a video output terminal 21.

Here, the operation of the signal amplification circuit 17 will be described more specifically. Since the level of the analog video signal 22 obtained by the solid-state video device 16 is minute, it is necessary to amplify the analog video signal 22 to a level at which signal processing can be performed while avoiding the influence of noise.

Therefore, before the analog video signal 22 is amplified by the amplifier 6, the band is limited by an integrating circuit composed of the resistor 2 and the variable capacitance diode 5 set to an appropriate capacitance by the control voltage 23 to reduce noise. The components are removed. In addition, when a dark portion is photographed by a camera, the level of the analog video signal 22 is particularly small, and thus the signal level may be amplified at a higher gain than usual. Therefore, if the analog video signal 22 is not amplified after the appropriate band limitation is performed by the integrating circuit including the resistor 2 and the variable capacitance diode 5, even the noise component is amplified, which adversely affects the image quality.

Before the analog video signal 22 is amplified as described above, the integrating circuit including the resistor 2 and the variable capacitance diode 5 is set to an appropriate frequency characteristic so that a good image quality can be obtained depending on a place where the camera takes a picture. Need to be done. For this purpose, the CPU 18 supplies the control voltage 23
Is set, the capacitance of the variable capacitance diode 5 is changed, and the frequency characteristic of the integrating circuit including the resistor 2 is changed as appropriate.

In the second embodiment using the signal amplifying circuit of the present invention, the target signal is an analog video signal.
For various sensor signals or modem signals, etc., these signals can be easily changed by changing the frequency characteristics of the integrating circuit composed of these by appropriately changing the capacitance of the variable capacitance diode by resistance and control voltage. Needless to say, it is possible to apply a stable and appropriate band limitation.

[0023]

According to the present invention, it is possible to realize a signal amplifying circuit capable of amplifying a signal with a simple hardware configuration, easily performing a stable and appropriate band limitation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a signal amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a signal amplification circuit according to the related art.

FIG. 3 is a diagram illustrating an example of a frequency characteristic of an integrating circuit;

FIG. 4 is a diagram showing an example of characteristics of a variable capacitance diode.

FIG. 5 is a block diagram showing a configuration of a signal amplifier circuit according to a second embodiment of the present invention.

[Explanation of symbols]

1: signal input terminal, 2: resistor, 3: coupling capacitor, 4: control voltage input terminal, 5: variable capacitance diode, 6: amplifier, 7: signal output terminal, 8: signal input terminal, 9: resistance, 10: capacitor, 11: transistor, 12: amplifier, 13: signal output terminal, 14:
Enable signal input terminal, 15: camera head, 16:
Solid-state imaging device, 17: signal amplification circuit, 18: CPU, 1
9: A / D converter, 20: digital signal processing circuit, 2
1: video signal output terminal, 22: analog video signal, 2
3: control voltage, 30: characteristic line, 31: characteristic line

 ──────────────────────────────────────────────────の Continued on front page F term (reference) 5C021 PA02 PA94 PA95 PA96 XA03 XA06 5J030 AA09 AB03 AB04 AB05 AC05 AC07 AC11 5J092 AA01 AA51 AA56 CA41 CA61 FA18 FA20 HA21 HA25 HA29 HA38 HA44 KA01 KA31 KA34 KA49 SA01 TA01

Claims (2)

[Claims] 1. A signal amplifying circuit for amplifying an analog signal to a desired level, comprising an integrating circuit comprising a resistor and a variable capacitance diode, wherein the integrating circuit amplifies the analog signal to a desired signal level. A video signal amplifying circuit which is arranged at a stage prior to the above, and amplifies the analog signal to a desired signal level after band-limiting the analog signal by the integration circuit. 2. The signal amplifying circuit according to claim 1, wherein the capacitance of the variable capacitance diode is made variable by an external control voltage to set a frequency characteristic of the integration circuit as desired, and the analog signal is converted to the analog signal. A signal amplifier circuit characterized in that the signal is amplified to a desired signal level after band limitation by an integrating circuit.