Voltage amplifying circuit

Details Voltage amplifying circuit Voltage amplifying circuit

2002-07-03

2004-08-31

Nguyen, Long (Department: 2816)

Amplifiers

With semiconductor amplifying device

Including gain control means

C330S281000, C330S141000

Reexamination Certificate

active

06784742

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to a voltage amplifying circuit, and more particularly to a voltage amplifying circuit that may be capable of having a selectable gain among a plurality of gain values.
BACKGROUND OF THE INVENTION
Referring to
FIG. 7
, a circuit schematic diagram of a conventional voltage amplifying circuit is set forth and given the general reference character
700
.
Conventional voltage amplifying circuit
700
has a signal input terminal
106
, gain changing terminal
108
, and a clamp pulse input terminal
109
. Conventional voltage amplifying circuit
700
also has a signal output terminal
103
.
Conventional voltage amplifying circuit
700
includes power supplies (
101
a
and
101
b
), voltage amplifiers (
102
a
and
102
b
), voltage clamp switches (
104
a
and
104
b
), clamp voltage sources (
105
a
and
105
b
), inverters (
110
to
112
), gain changing switches (
113
and
114
), and capacitors (C
101
to C
103
).
Voltage amplifier
102
a
includes n-type MOS (metal-oxide-semiconductor) transistors (
120
a
and
121
a
). Voltage amplifier
102
b
includes n-type MOS transistors (
120
b
and
121
b
). Voltage amplifiers (
102
a
and
102
b
) have identical gains.
Gain changing switches (
113
and
114
) are n-type MOS transistors.
Because a capacitor C
102
is disposed between a gate of n-type MOS transistor
120
a
and ground, a gain of a signal from signal input terminal
106
to a signal output terminal
103
through voltage amplifier
102
a
is smaller than the gain of a signal from signal input terminal
106
to signal output terminal
103
through voltage amplifier
102
b.
When a high voltage (such as 5 volts) is applied to gain changing terminal
108
, gain changing switch
113
turns off and gain changing switch
114
turns on. Thus, a voltage gain path from signal input terminal
106
to signal output terminal
103
through voltage amplifier
102
b
is selected and the gain of conventional voltage amplify circuit
700
becomes high. When a low voltage (such as 0 volts) is applied to gain changing terminal
108
, gain changing switch
114
turns off and gain changing switch
113
turns on. Thus, a voltage gain path from signal input terminal
106
to signal output terminal
103
through voltage amplifier
102
a
is selected and the gain of conventional voltage amplify circuit
700
becomes low. In this way, the gain of conventional voltage amplifying circuit
700
can be selected or changed over.
Referring now to
FIG. 8
, a circuit schematic diagram of a conventional voltage amplifying circuit is set forth and given the general reference character
800
.
Conventional voltage amplifying circuit
800
has a signal input terminal
206
, gain changing terminal
208
, and a clamp pulse input terminal
209
. Conventional voltage amplifying circuit
800
also has a signal output terminal
203
.
Conventional voltage amplifying circuit
800
includes power supplies (
201
a
and
201
b
), voltage amplifiers (
202
a
and
202
b
), voltage clamp switches (
204
a
and
204
b
), clamp voltage sources (
205
a
and
205
b
), inverters (
210
to
212
), gain changing switches (
213
and
214
), and capacitors (C
201
and C
202
).
Voltage amplifier
202
a
includes n-type MOS transistors (
220
a
and
221
a
). Voltage amplifier
202
b
includes n-type MOS transistors (
220
b
and
221
b
). Voltage amplifier
202
a
has a gain that is larger than voltage amplifier
202
b
.
FIG. 9
is a graph illustrating voltage transfer characteristics of voltage amplifiers (
202
a
and
202
b
). The gain can be ascertained by the slope of the transfer characteristics. As illustrated in
FIG. 9
, voltage amplifier
202
a
has a higher gain than voltage amplifier
202
b.
Referring once again to
FIG. 8
, when a high voltage (such as 5 volts) is applied to gain changing terminal
208
, gain changing switch
213
turns off and gain changing switch
214
turns on. Thus, a voltage gain path from signal input terminal
206
to signal output terminal
203
through voltage amplifier
202
b
is selected and the gain of conventional voltage amplify circuit
800
becomes low. When a low voltage (such as 0 volts) is applied to gain changing terminal
208
, gain changing switch
214
turns off and gain changing switch
213
turns on. Thus, a voltage gain path from signal input terminal
206
to signal output terminal
203
through voltage amplifier
202
a
is selected and the gain of conventional voltage amplify circuit
800
becomes high. In this way, the gain of conventional voltage amplifying circuit
800
can be selected or changed over.
Referring now to
FIG. 10
, a circuit schematic diagram of yet another conventional voltage amplifying circuit is set forth and given the general reference character
1000
.
Conventional voltage amplifying circuit
1000
has a signal input terminal
306
, gain changing terminal
308
, and a clamp pulse input terminal
309
. Conventional voltage amplifying circuit
1000
also has a signal output terminal
303
.
Conventional voltage amplifying circuit
1000
includes a power supply
301
, a voltage amplifier
302
, a voltage clamp switch
304
, a clamp voltage source
305
, inverters (
310
and
311
), and a capacitor C
301
.
Voltage amplifier
302
includes n-type MOS transistors (
320
to
322
).
In voltage amplifier
302
, n-type MOS transistors (
320
and
321
) are used as resistors or loads. N-type MOS transistor
321
is turned on or off to select or change over the gain.
When a high voltage (such as 5 volts) is applied to gain changing terminal
308
, n-type MOS transistor
321
turns off. Thus, the gain of conventional voltage amplify circuit
1000
becomes low. When a low voltage (such as 0 volts) is applied to gain changing terminal
308
, n-type MOS transistor
321
turns on. Thus, the gain of conventional voltage amplify circuit
1000
becomes high. In this way, the gain of conventional voltage amplifying circuit
1000
can be selected or changed over.
In conventional voltage amplifying circuit
700
of
FIG. 7
, even the operating speed may not change for the two selectable gains because both voltage amplifiers (
102
a
and
102
b
) have the same gain. However, in conventional voltage amplifying circuit
800
of
FIG. 8
, the operating speed can differ when the gain is changed over because voltage amplifiers (
202
a
and
202
b
) have different gains. In conventional amplifying circuits (
700
and
800
), the circuit size can be relative large because two voltage amplifiers are used. Also, because two voltage amplifiers are used and enabled at all times (an output from one of the two voltage amplifiers is selected), power consumption is relatively large.
On the contrary, conventional voltage amplifying circuit
1000
uses only one voltage amplifier. Thus, the circuit area and power consumption may be reduced as compared with conventional voltage amplifying circuits (
700
and
800
). However, in conventional voltage amplifying circuit
1000
, the amount of current flowing in voltage amplifier
302
varies in accordance with whether n-type MOS transistor
321
is on or off. The change in current causes change in operating speeds and power consumption. The operating speed and power consumption changes more as the gain variation ratio (ratio of the high gain to the low gain) becomes larger. Therefore, conventional voltage amplifying circuit
1000
may be effective for a case where there is a small gain and a gain variation ratio is only about two. However, for large gains and large gain ratios, the power consumption may be large and the operation speed differences may be relatively large.
In view of the above discussion, it would be desirable to provide a voltage amplifying circuit, which may have a reduced circuit area and/or power consumption. It would also be desirable to provide a voltage amplifying circuit in which operating speed variation and/or power consumption variation is suppressed when a gain is changed over or switched.
SUMMARY OF THE INVENTION
According to the present embodiments, a voltage amplifyin

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