Amplifiers – With semiconductor amplifying device – Including push-pull amplifier
Reexamination Certificate
2001-06-01
2003-07-15
Lam, Tuan T. (Department: 2816)
Amplifiers
With semiconductor amplifying device
Including push-pull amplifier
C330S271000
Reexamination Certificate
active
06593813
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a negative feed-back amplifier and more particularly to a negative feed-back amplifier that can be suitably used in a video IF (Intermediate Frequency) amplifier installed on a video signal circuit of a television and to a method for negative feed-back.
The present application claims priority of Japanese Patent Application No. 2000-166868 filed on Jun. 2, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
As shown in
FIG. 8
, a picture signal related circuit of a television is provided with a tuner
1
, a band-pass filter (hereinafter referred to as a BPF
2
), a local oscillator
3
, a mixer
4
, an immediate frequency preamplifier (hereinafter referred to as an IF frequency preamplifier
5
), a condenser
6
, and an intermediate frequency main amplifier (hereinafter referred simply to as an IF main amplifier
7
). The IF preamplifier
5
, the condenser
6
, and a negative feed-back amplifier (the IF main amplifier
7
) make up a video IF amplifier.
FIG. 9
is a circuit diagram showing electrical configurations of the IF main amplifier
7
shown in FIG.
8
. The IF main amplifier
7
is provided with a bipolar transistor (hereinafter referred to a transistor
7
a
), a resistor
7
b
, a resistor
7
c
, a transistor
7
d
, a transistor
7
e
, a resistor
7
f
, a resistor
7
g
, and a resistor
7
h.
In the picture signal related circuit, a receiving signal received by an antenna (not shown) is input to the tuner
1
and a video intermediate frequency signal V
1
is output from the tuner
1
. The video intermediate frequency signal V
1
is then input to the BPF
2
and an output signal V
2
in a predetermined frequency band is output. The output signal V
2
is mixed with an output signal V
3
fed from the local oscillator
3
by the mixer
4
and an output signal V
4
is output from the mixer
4
. The output signal V
4
is amplified by the IF preamplifier
5
and an output signal V
5
is output from the IF preamplifier
5
. The output signal V
5
is input to the IF main amplifier
7
through the condenser
6
and amplified and then a video detecting signal “OUT” is output from the IF main amplifier
7
. The video detecting signal “OUT” is transmitted to a video detecting amplifier (not shown). In this case, as shown in
FIG. 9
, an output impedance of the IF main amplifier
7
is determined by the resistor
7
f
and a resistance of the resistor
7
f
is set to a value that does not cause the video detecting signal “OUT” to occur, with considerations given to a state of matching with a characteristic impedance of a transmission line connected to an output of the IF main amplifier
7
and with an input impedance of the video detecting amplifier (not shown). Moreover, the video detecting signal “OUT” is fed back to a base of the transistor
7
a
through the resistor
7
h.
However, in the conventional IF main amplifier
7
, since, depending on set values of the resistors
7
b
,
7
c
,
7
f
, and
7
g
, a base potential of the transistor
7
a
becomes too high and a dynamic range in a first stage becomes small; if an input signal “IN” is large, in some cases, a distortion of the video detecting signal “OUT” increases. This presents a problem in that an image quality of the television deteriorates.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a negative feed-back amplifier and a method for negative feed-back which are capable of preventing a distortion of a signal even if an input signal is large.
According to a first aspect of the present invention, there is provided a negative feed-back amplifier including;
a push-pull amplifier made up of bipolar transistors and used to amplify an input signal and to output an output signal; and
a negative feed-back circuit used to bias a base of a bipolar transistor at an initial stage of the push-pull amplifier by using a negative feed-back signal produced by attenuation of the output signal at a predetermined feedback ratio.
According to a second aspect of the present invention, there is provided a negative feed-back amplifier including:
a push-pull amplifier made up of bipolar transistors and used to amplify an input signal and to output an output signal; and
a negative feed-back circuit used to bias a base of a bipolar transistor at an initial stage of the push-pull amplifier by using a negative feed-back signal produced by attenuation of a signal corresponding to the output signal at a predetermined feedback ratio.
According to a third aspect of the present invention, there is provided a negative feed-back amplifier including:
a phase inverter amplifier used to amplify an input signal and to produce a reversed signal of a phase opposite to the input signal and to produce a non-reversed signal being in phase with the input signal;
a push-pull output circuit used to produce an output signal of a phase opposite to the input signal by inputting the reversed signal at high input impedance and outputting the reversed signal at low output impedance and outputting the non-reversed signal in a reversed state;
a negative feed-back circuit used to produce a negative feed-back signal by inputting the output signal and to add the negative feed-back signal to the input signal; and
wherein the negative feed-back circuit is provided with a feedback ratio setting circuit used to attenuate the output signal at a predetermined feedback ratio and to produce the negative feed-back signal.
According to a fourth aspect of the present invention, there is provided a negative feed-back amplifier including:
a phase inverter amplifier used to amplify an input signal and to produce a reversed signal of a phase opposite to the input signal and to produce a non-reversed signal being in phase with the input signal;
a push-pull output circuit used to produce an output signal of a phase opposite to the input signal by inputting the reversed signal at high input impedance and outputting the reversed signal at low output impedance and outputting the non-reversed signal in a reversed state;
a negative feed-back circuit used to produce a negative feed-back signal by inputting the output signal and to add the negative feed-back signal to the input signal; and
wherein the negative feed-back circuit has an impedance converter used to produce a feed-back signal by inputting the output signal at high input impedance and outputting the output signal at low output impedance and a feed-back ratio setting circuit used to produce the negative feed-back signal by attenuating the feed-back signal at a predetermined feed-back ratio.
According to a fifth aspect of the present invention, there is provided a negative feed-back amplifier including:
a phase inverter amplifier used to amplify an input signal and to produce a reversed signal of a phase opposite to the input signal;
a push-pull output circuit used to produce an output signal of a phase opposite to the input signal by inputting the reversed signal at high input impedance and outputting the reversed signal at low output impedance;
a negative feed-back circuit used to produce a negative feed-back signal by inputting the output signal and to add the negative feed-back signal to the input signal; and
wherein the negative feed-back circuit is provided with a feedback ratio setting circuit used to attenuate the output signal at a predetermined feedback ratio and to produce the negative feed-back signal.
According to a sixth aspect of the present invention, there is provided a negative feed-back amplifier including:
a phase inverter amplifier used to amplify an input signal and to produce a reversed signal of a phase opposite to the input signal;
a push-pull output circuit used to produce an output signal of a phase opposite to the input signal by inputting the reversed signal at high input impedance and outputting the reversed signal at low output impedance;
a negative feed-back circuit used to produce a negative feed-back signal by inputting the output signal and to
Hayes & Soloway P.C.
Lam Tuan T.
NEC Compound Semiconductor Devices Ltd.
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