Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2002-10-22
2004-03-09
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C363S059000
Reexamination Certificate
active
06703890
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a charge pump booster circuit for supplying a voltage different from a source voltage and a voltage supply circuit containing a driver circuit for driving the charge pump booster circuit.
BACKGROUND OF THE INVENTION
Usually, a DC—DC converter equipped with a switching power source or a charge pump type booster circuit is used to generate a voltage having a level different from that of a source voltage. A voltage higher than the source voltage or a negative voltage can be generated using these circuits.
For example, the frequency range of the TV tuner of a TV receiver can be adjusted (tuning) by changing the tuning voltage applied to the variable capacitor (variable capacity element) of the voltage control oscillator circuit (VCO) according to the channel to be received. A voltage of 30 V or so may be needed for said tuning voltage depending on the frequency band of the signal received.
In recent years, TV tuners have been used widely for automobile TVs and personal computers (personal computer), for example, where compactness, light weight, and portability are often demanded. Thus, a system is needed in which the tuning voltage needed for the TV tuner is generated inside of the device instead of supplied from the outside. A charge pump booster circuit is widely utilized as a voltage generator circuit to this end.
FIG. 4
shows an example configuration of a popular charge pump type booster circuit. As illustrated, said booster circuit is configured with oscillator circuit
10
, charge pump driver circuit
20
, and charge pump circuit
30
. Configurations of the respective partial circuits and their functions will be explained below.
As shown in the figure, oscillator circuit
10
is usually configured with crystal oscillator XTL, capacitor C
1
, and oscillation amplifier OSC.
Charge pump driver circuit
20
is configured with comparator CMP and buffers BUF
1
and BUF
2
which supply driving currents I
S1
and I
S2
to charge pump circuit
30
according to the output signal of comparator CMP.
Charge pump circuit
30
is configured with multi-stage diodes D
1
, D
2
, . . . , Dn connected in series between source voltage V
CC
supplying terminal T
1
and output terminal T
2
, multiple capacitors C
p1
, C
p2
, . . . provided to serve as a charge pump, output capacitor C
OUT
, and multi-stage Zener diodes ZD
1
, . . . , ZDm connected in series between output terminal T
OUT
and ground potential GND.
Capacitors C
p1
, C
p2
, . . . for the charge pump are connected to output terminals of diodes D
1
, D
2
, . . . at one end, and their other ends are connected to output terminals of buffers BUF
1
and BUF
2
alternately.
FIG. 5
is a circuit diagram showing the internal configurations of oscillator circuit
10
and charge pump driver circuit
20
.
As illustrated, oscillator circuit
10
is configured with crystal oscillator XTL, capacitor C
1
, and oscillation amplifier OSC; and oscillation amplifier OSC is further configured with npn transistors P
3
and P
4
, capacitors C
2
and C
3
, and resistor elements R
1
through R
6
.
Crystal oscillator XTL and capacitor C
1
are connected in series between oscillation signal output terminal T
3
and ground potential GND.
In addition, npn transistors P
1
and P
2
diode-connected between the feed line of source voltage V
CC
and node ND
1
are connected in series.
In oscillation amplifier OSC, the base of transistor P
3
is connected to terminal T
3
, its collector is connected to ND
1
, and the emitter is grounded via resistor element R
3
. In addition, capacitors C
2
and C
3
are connected in series between terminal T
3
and ground potential GND, and the junction of capacitors C
2
and C
3
is connected to the emitter of transistor P
3
.
In addition, resistor elements R
4
and R
5
are connected in series between node ND
1
and ground potential GND, the collector of transistor P
4
is connected to node ND
1
, the base is connected to the junction of resistor elements R
4
and R
5
, and the emitter is grounded via resistor element R
6
.
Oscillator circuit
10
with the configuration is oscillated at an oscillation frequency unique to crystal oscillator XTL, and oscillation voltage V
osc
is output from terminal T
3
. In addition, the gain of said oscillator circuit is determined based on the capacitances of capacitors C
2
and C
3
.
In charge pump driver circuit
20
, the differential circuit comprising npn transistors P
5
and P
6
and the differential circuit comprising npn transistors P
8
and P
9
constitute comparator CMP shown in FIG.
4
. In addition, pnp transistors Q
1
and Q
2
and npn transistors P
11
, P
12
, P
13
, and P
14
constitute buffers BUF
1
and BUF
2
, respectively.
In the charge pump driver circuit
20
, comparator CMP compares oscillation voltage V
OSC
of terminal T
3
of oscillator circuit
10
and the base voltage of transistor P
4
, generates an oscillation signal according to the result of said comparison, and outputs it to buffers BUF
1
and BUF
2
. As a result, charge pump driving currents I
S1
and I
S2
having inverted phases with respect to each other are output from buffers BUF
1
and BUF
2
.
Driving currents I
S1
and I
S2
output from buffers BUF
1
and BUF
2
are output into capacitors C
p1
, C
p2
, . . . provided in charge pump circuit
30
. Thus, capacitors C
p1
, C
p2
, . . . are discharged and recharged alternately repeatedly at charge pump circuit
30
, so that a voltage higher than source voltage V
CC
is output to output terminal T
OUT
. Furthermore, voltage V
OUT
of output terminal T
OUT
is smoothened by output capacitor C
OUT
and sustained at a desired voltage by multi-stage Zener diodes ZD
1
, . . . , ZDm connected in series.
In the charge pump booster circuit, the number of boosting steps is decided according to source voltage V
CC
and desired output voltage V
OUT
. Furthermore, in general, the number of boosting steps is set so as to supply a boosted voltage higher than desired output voltage V
OUT
in order to assure sufficient current driving performance for a load circuit, and the current driving performance of the boosting circuit can be assured by regulating output voltage V
OUT
at a desired voltage value.
In the conventional charge pump type booster circuit, another feedback loop is formed in charge pump driver circuit
20
via the source impedance in addition to the feedback loop of oscillator circuit
10
. In particular, when the impedance of the source line is high, parasitic oscillation is induced by the feedback loop of charge pump driver circuit
20
. As a result, oscillator circuit
10
can no longer perform a normal oscillation operation, and the frequencies of the driving currents output from buffers BUF
1
and BUF
2
are determined by the oscillation frequency of the parasitic oscillation.
Normally, the oscillation frequency of oscillator circuit
10
is controlled by the frequency unique to crystal oscillator XTL. Because the buffers and charge pump circuit
30
are designed in accordance with the oscillation frequency of the oscillator circuit and the oscillation frequency of the parasitic oscillation is determined based on the characteristic of the feedback loop which induces the parasitic oscillation, the parasitic oscillation is considered to oscillate at an oscillation frequency different from the oscillation frequency of the crystal oscillator XTL. Thus, sufficient current can no longer be supplied to charge pump circuit
30
, or the frequency of the driving currents becomes either lower or higher than the reference value required by charge pump circuit
30
, and voltage V
OUT
output from charge pump circuit
30
cannot reach the desired voltage, resulting in a disadvantage that the desired current cannot be supplied to the load circuit.
The present invention was created in the light of such situation, and its objective is to present a voltage supply circuit by which the parasitic oscillation of the charge pump driver circuit can be restrained, the charge pump driving currents can be generated at a stable o
Brady III W. James
Cunningham Terry D.
Kempler William B.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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