Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2001-11-05
2002-07-23
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S009000, C330S053000, C330S055000, C330S064000
Reexamination Certificate
active
06424219
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an operational amplifier, especially to one to be used in a device for driving a liquid crystal panel.
2. Description of the Prior Art
Typically, a liquid crystal panel requires a writing operation at a speed of several tens of frames (several tens of sheets) per second. An output signal generated from a drive circuit of the liquid crystal panel is provided for performing an AC drive on the potential of a common electrode for each of scanning lines or frames. Referring now to
FIGS. 7 and 8
, we will describe an operational amplifier and a drive circuit of the conventional liquid panel, which perform such an AC drive on the potential of common electrode.
FIG. 7
is a circuit diagram that illustrates an example of the conventional operational amplifier for driving a liquid panel. As shown in the figure, the conventional operational amplifier
1
a
comprises differential input stage circuits
2
,
3
, output stage field effect transistors (FETS)
11
-
14
, and drive stage circuits
4
,
5
, and it may be functionally used as a converting circuit for an output impedance. In the operational amplifier
1
a
, each of the differential input circuits
1
,
3
is connected between a high-potential side power source (VDD)
8
and a low-potential side power source (VSS)
9
. The differential input circuit
1
(
3
) amplifies the differential potential between an analog input supplied to a positive input terminal
11
(
13
) and an analog input supplied to a negative input terminal
12
(
14
) and generates an output to a differential input stage output terminal
101
(
102
). One end of the FET
11
(
13
) is connected to the high-potential side power source
8
and the other end thereof is connected to an output terminal VO
1
(VO
2
) of the operational amplifier
1
a
. In addition, one end of the FET
12
(
14
) is connected to the low-potential side power source (VSS)
9
and the other end thereof is connected to an output terminal VO
1
(VO
2
) of the operational amplifier
1
a
. Each of the drive stage circuits
4
,
5
is also connected between the high-potential side power source
8
and the lower-potential-power source
9
. The drive stage circuit
4
(
5
) supplies a drive output signal to the FETs
11
and
12
(
13
and
14
) through output terminals
105
and
106
(
107
and
108
) on the basis of the differential outputs from the output terminals
101
,
102
, respectively.
Each of the differential input stage circuits
2
,
3
of the operational amplifier
1
a
is able to acquire the input range from a level at the low-potential side power source (VSS) to a level at the high-potential side power source (VDD). The output stage FET
11
has a gate electrode connected to an output terminal
105
of the drive stage circuit
4
, a source electrode connected to a high-potential side power source
8
, and a drain electrode connected to the output terminal VO
1
. Similarly, the output stage FET
13
has the connections to the drive stage circuit
5
and the output terminal VO
2
. Similarly, the output stage FETs
12
,
14
have their connections to the low-potential side power source
9
and the output terminal VO
2
.
FIG. 8
is a circuit diagram that illustrates the configuration of an example of the circuit for driving the liquid crystal panel (hereinafter, simply referred to as a LCP-drive circuit) in which the conventional operational amplifier is used. As shown in the figure, the LCP-drive circuit
40
a
comprises: positive and negative side digital-to-analog (DA) converters
41
,
42
that translate digital signals to analog signals with respect to input signals on the positive and negative sides, respectively; switching means
43
,
44
for switching the translated outputs from the DA converters using the predetermined input control signals from the outside; the operational amplifier (see
FIG. 7
) for the operationally amplifying the outputs switched by the switching means
43
,
44
; and switching means
47
,
48
for switching the outputs VO
1
, VO
2
from the operational amplifier using control inputs from the outside and then supplying the outputs to output terminals OUT
1
, OUT
2
, respectively.
The DA converters
41
,
42
perform digital to analog transformation to obtain analog data of middle-potential to high-potential side power source and analog data of middle-potential to low-potential side power source, respectively, depending of input digital data. Each of the switching means
43
,
44
,
47
,
48
is constructed of a pair of switches S and Sb that perform different operations opposed to each other. Furthermore, the operational amplifier creates the negative feedback of signals, so that each of the outputs VO
1
, VO
2
is feed backed to negative side inputs VI
2
, VI
4
against positive side inputs VI
1
, VI
3
, respectively.
The LCP-drive circuit
40
a
can be actuated and operated as follows. At first, analog signals from the positive side DA converter
51
and analog signals from the negative side DA converter
42
are respectively introduced into the operational amplifier
1
a
when each switch S in the switching means
43
,
44
,
47
,
48
is switched on (at this time, the switch Sb is switched off). Then, each input signal is subjected to an impedance conversion and is then generated as an output to the output terminal OUT
1
or OUT
2
through the switching means
47
or
48
. In general, a plurality of output terminals is provided on the LCP-drive circuit
40
a
for driving each element of the liquid crystal panel. For simplifying the illustration and for the sake of expediency, the circuit
40
a
is described as one having two output terminals.
Likewise, when each switch Sb in the switching means
43
,
44
,
47
,
48
is switched on (at this time, the switch S is switched off), analog signals selected with the positive side DA converter
41
is subjected to an impedance conversion and is then generated as an output to the output terminal OUT
2
, while those selected with the negative side DA converter
42
is subjected to an impedance conversion and is then generated as an output to the output terminal OUT
1
.
The LCP-drive circuit
40
a
is able to generate several tens of outputs of positive- or negative-side analog signals (i.e., to perform several tens of writing operations on the panel). If the scanning line is switched from one to another, then the terminal from which the negative side analog signals are outputted and the terminal from which the positive side analog signals are outputted are replaced with each other to operate with alternating current.
FIG. 9
is a timing chart of an output waveform of the conventional LCP-drive circuit. As shown in this figure, if the opposite switching operations of switches S, Sb are performed, signal waveforms for the discharge of the liquid crystal panel to be outputted to the output terminals OUT
1
, OUT
2
may be changed from the voltage at the high-potential side power source VDD to the voltage at the low-potential side power source VSS and from the voltage at the low-potential side power source VSS to the voltage at the high-potential side power source VDD, respectively.
The liquid crystal panel described above is provided as a capacitive load. As for driving such a liquid crystal panel due to the change in analog signals to be inputted, therefore, it means that the capacitive load of the panel can be charged and discharged.
As described above, furthermore, the LCP-drive circuit repeats the operation in which the positive- or negative-side voltage is outputted several ten times, the output polarity is then replaced, and the negative- or positive-side voltage is subsequently outputted several ten times.
The charge and discharge of the capacitive load is performed between the high-potential side power source and the low-potential side power source, so that a power consumption P per one output can be expressed by the following equation.
P=C×f×Vpp×VDD
Wherein VDD denotes the potential difference betwee
Choe Henry
NEC Corporation
Pascal Robert
LandOfFree
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