Semiconductor integrated circuit device

Details Semiconductor integrated circuit device Semiconductor integrated circuit device

2002-03-06

2003-02-11

Cunningham, Terry D. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Current driver

C327S170000, C327S374000, C327S376000

Reexamination Certificate

active

06518804

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, which includes a driver circuit for driving a capacitive load based on an input signal, and an power supply transistor for supplying a power supply voltage to said driver circuit. In particular, it relates to a semiconductor device such as a driver circuit for a common terminal of a liquid crystal display device, where the output signal amplitude of said driver circuit needs to be adjusted based on the power source voltage.
2. Description of the Prior Art
An example of a conventional semiconductor integrated circuit device of this type is described below while referencing FIG.
8
.
FIG. 8
is a semiconductor integrated circuit device for driving a common terminal of a liquid crystal display device used in, for example, mobile telephones. In
FIG. 8
,
100
denotes to a semiconductor integrated circuit device, wherein external power source V
CC
is connected to power source terminal
1
, ground terminal
2
is connected to ground, input signal Vin is supplied to input terminal
3
, and capacitive load CL is connected to output terminal
4
. Semiconductor integrated circuit device
100
includes internal power source circuit
10
, which generates a desired internal power source voltage V
HL
from external power source voltage V
CC
, and switching circuit
20
, which performs switching control in conformity with input signal Vin outputting internal power source voltage V
HL
to output terminal
4
.
Internal power source circuit
10
is configured such that external power source voltage V
CC
is divided into a desired voltage level at the connection point of resistor
11
and resistor
12
, which are connected in series, and is output as internal power source voltage V
HL
to switching circuit
20
via operational amplifier
13
. As shown by the specific structural example illustrated in
FIG. 9
, operational amplifier
13
is configured such that it has P-channel MOSFET
14
and N-channel MOSFET
15
, which are connected in series, at the output stage; the source of MOSFET
14
is connected to power source terminal
1
; the source of MOSFET
15
is connected to ground terminal
2
; and internal power source voltage V
HL
is output from the junction of MOSFET
14
and MOSFET
15
.
Switching circuit
20
is configured such that it has a CMOS structure comprising P-channel MOSFET
21
and N-channel MOSFET
22
, wherein internal power source voltage V
HL
is supplied to the source of MOSFET
21
and ground terminal
2
is connected to the source of MOSFET
22
. With this structure, when input signal Vin, which is from input terminal
3
, is supplied to the respective gates of MOSFET
21
and MOSFET
22
via inverter
23
, MOSFET
21
and MOSFET
22
are on/off controlled to output internal power source voltage V
HL
from the junction of MOSFET
21
and MOSFET
22
to output terminal
4
as output voltage Vout.
As for the operation of semiconductor integrated circuit device
100
having the above-mentioned structure, once external power source voltage V
CC
is supplied to power source terminal
1
, external power source voltage V
CC
is divided into a desired voltage level at the junction of resistor
11
and resistor
12
, and the resulting voltage is output from internal power supply circuit
10
as internal power supply voltage V
HL
via operational amplifier
13
. While in the state where internal power supply voltage V
HL
is being output from internal power supply circuit
10
, as input signal Vin goes from a “L=0” level to a “H=V
CC
” level and MOSFET
21
of switching circuit
20
turns on, as shown in
FIG. 10
, electrical current flows from internal power source
10
via MOSFET
21
to capacitive load CL, which is connected to output terminal
4
, and output voltage Vout climbs up to internal power source voltage V
HL
.
In the semiconductor integrated circuit device described above, while output voltage Vout climbs up to input power source voltage V
HL
, the electric potential at the gate of MOSFET
21
is at level “L”, and MOSFET
21
is turned on completely. On the other hand, while operational amplifier
13
of internal power source circuit
10
is in the state where external.power source voltage V
CC
is divided at the junction of resistor
11
and resistor
12
thereby being supplied to the non-inverting input terminal, since the electric potential at the gate of MOSFET
14
does not reach level “L=0”, even though MOSFET
14
may be on, it is not turned on completely. At this point, for example, if the size of MOSFET
14
is designed to be the same size as MOSFET
21
, although MOSFET
21
may be turned on completely, since MOSFET
14
is not turned on completely, the electric current capacity of MOSFET
14
is insufficient when compared to the electric current capacity of MOSFET
21
. In this case, the operating speed of operational amplifier
13
in response to changes in electric current is slow and cannot keep up with high-speed electric current changes occurring during switching. Accordingly, as shown in
FIG. 10
, there is a problem, wherein after internal power source voltage V
HL
has temporarily fallen, since the rising waveform up to the desired voltage has a gentle slope, the rising waveform of the output voltage Vout has also a gentle slope.
When a semiconductor integrated circuit device is used as a driver of liquid crystal display device, the desired display cannot be achieved. In order to speed up the operational speed in response to electric current changes in operational amplifier
13
, a larger size of output transistor
14
included in operational amplifier
13
may be used; however, there is a problem with the semiconductor integrated circuit device having a larger chip size.
SUMMARY OF THE INVENTION
The present invention has come about in consideration of the problems described above and aims to provide a semiconductor integrated circuit device in which switching speed is increased by increasing electric current capacity of an internal power source circuit the instant a switching circuit is switched on.
A semiconductor integrated circuit device according to the present invention, comprises:
a driver circuit driving a capacitive load responding to an input signal;
a power source transistor biased so as to supply a fixed voltage to a power supply terminal of said drive circuit; and
a control circuit detecting a change in said input signal, forcibly shifting bias of said power source transistor and increasing an electrical current supply capacity of said power source transistor when said input signal changes to drive said capacitive load with electric current supplied from said power source transistor.


REFERENCES:
patent: 5742193 (1998-04-01), Colli et al.
patent: 6262607 (2001-07-01), Suzuki
patent: 4-259115 (1992-09-01), None

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