Low ripple scalable DC-to-DC converter circuit

Details Low ripple scalable DC-to-DC converter circuit Low ripple scalable DC-to-DC converter circuit

2002-06-03

2003-09-09

Riley, Shawn (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S280000

Reexamination Certificate

active

06617832

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a method and circuit for providing a low ripple regulated output voltage of greater magnitude than an unregulated input voltage applied to the circuit.
FIG. 1A
shows a conventional charge pump
1
in which an input voltage V
IN
is applied between an input terminal
2
and the ground conductor
3
. During a first phase, a pair of switches
4
and
8
are closed to connect the upper terminal
5
and the lower terminal
9
of a pump capacitor C
PMP
to V
IN
and to ground, respectively. A pair of switches
6
and
10
each have a terminal connected to terminal
5
and to terminal
9
, respectively. Both of switches
6
and
10
are open during the first phase. The pump capacitor C
PMP
therefore is charged to V
IN
during the first phase. During a second phase, switches
4
and
8
are open, and switches
6
and
10
are closed, as shown in FIG.
1
B. Switch
6
connects the upper terminal
5
of C
PMP
to output conductor
7
, which is connected to the upper terminal of output capacitor C
OUT
. Switch
10
connects the lower terminal
9
of C
PMP
to V
IN
. As the first and second phases are repeated, the output voltage V
OUT
on conductor
7
increases to
2
V
IN
. However, conventional charge pump
1
produces a large ripple voltage, typically of approximately 50 millivolts amplitude, in V
OUT
. This is because pump capacitor C
PMP
is repetitively connected and disconnected between V
IN
and V
OUT
, causing a ripple voltage proportional to the ratio between C
PMP
and C
OUT
.
In some applications, a much lower level of ripple voltage amplitude may be required, for example, in a DC-to-DC converter used as a power supply for a precision voltage reference, a low-noise, low-offset operational amplifier, or any application sensitive to noise or perturbations on the power supply voltage. Reducing the ripple voltage by filtering may be unduly impractical and expensive because of the size and cost of the components needed to implement the filter. Some applications of low noise DC-to-DC converter circuits include their use in cell phones, PDAs (personal digital assistants), VCO (voltage controlled oscillator) and PLL (phase locked loop) power supplies, and smart card readers.
FIG. 2
shows a conventional linear voltage regulator
12
in which an operational amplifier
13
has its (−) input connected to a reference voltage V
REF
and output connected to the gate of a P-channel pass transistor
14
. The source of pass transistor
14
is connected by conductor
17
to an unregulated input voltage V
IN
. The drain of pass transistor
14
is connected by conductor
15
to produce a regulated output voltage V
OUT
on one terminal of an output capacitor C
OUT
having to the terminal connected to ground. A feedback circuit includes a resistor R
F
and a resistor R
S
connected in series between V
OUT
and ground. The junction between resistor R
F
and resistor RS is connected by conductor
16
to the (+) of operational amplifier
13
. Regulator
12
always produces a value of V
OUT
having a lower magnitude than V
IN
.
Linear Technology Corporation markets a linear regulator circuit, the LTC 1682, that utilizes a charge pump connected to supply the input voltage of a linear regulator circuit similar to the regulator shown in FIG.
2
. Although this linear regulator circuit is referred to in its product specification sheet as a “low noise linear regulator”, it nevertheless has the shortcoming that it produces a large ripple voltage (i.e., a large noise voltage) superimposed on the regulated output voltage produced.
Thus, there is an unmet need for an improved charge pump circuit that is capable of boosting an input voltage so as to provide a boosted output voltage having a much lower ripple voltage than conventional charge pump circuits.
There also is an unmet need for an improved DC-to-DC converter circuit that is capable of boosting an input voltage to provide a boosted output voltage having a much lower ripple voltage than conventional DC-to-DC converter circuits.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an improved charge pump circuit that is capable of boosting an input voltage so as to provide a boosted output voltage having a much lower ripple voltage than conventional charge pump circuits.
It is another object of the invention to provide an improved charge pump circuit that is capable of boosting an input voltage so as to provide a boosted output voltage having a low ripple voltage, which charge pump circuit is conveniently scalable to boost the input voltage to produce a higher amplitude, low ripple output voltage by using multiple pump capacitors.
It is another object of the invention to provide a DC-to-DC converter that is capable of boosting an input voltage so as to provide a boosted output voltage having a low ripple voltage, including a charge pump circuit that is conveniently scalable to boost the input voltage of the DC-to-DC converter to produce a higher amplitude, low ripple output voltage.
It is another object of the invention to provide an improved DC-to-DC converter circuit that is capable of boosting an input voltage so as to provide a boosted output voltage having a low ripple voltage, which DC-to-DC converter circuit is conveniently scalable to boost the input voltage to produce a higher amplitude, low-ripple output voltage by using an inductor and capacitor.
Briefly described, and in accordance with one embodiment thereof, the invention provides a DC-to-DC conversion circuit having an input conductor for receiving an input voltage (V
IN
) and an output conductor (
15
) for conducting an output voltage (V
OUT
), the DC-to-DC conversion circuit, including a pass transistor (
14
) having a first electrode coupled to receive the input voltage (V
IN
) and a second electrode coupled to a first conductor (
17
). An amplifier circuit (
13
) has a first input coupled to receive a first reference voltage (V
REF
) and an output coupled to a control electrode of the pass transistor. Level shifting circuitry (
18
) is coupled to the first conductor (
17
), the output conductor (
15
), the input conductor, and a conductor conducting a second reference voltage (GND), wherein the level shifting circuitry is capable of providing energy needed to boost the output voltage to a required level. A feedback circuit is coupled between the output conductor (
15
) and a second input of the amplifying circuit (
13
).
In one embodiment, the invention provides a circuit for boosting an input voltage (V
IN
) to provide a low ripple output voltage (V
OUT
) by regulating flow of current between a source of the input voltage (V
IN
) and a circuit node (
17
) in response to a feedback signal (
16
) representative of the output voltage (V
OUT
). A charge pump circuit operates to repetitively charge a pump element (C
PMP
or L
PMP
) to a voltage determined by the input voltage (V
IN
) and redistribute charge between the pump element and a level-shifting capacitor (C
LS
) coupled between the circuit node (
17
) and an output conductor (
15
) conducting the output voltage (V
OUT
) so as to maintain the boosted output voltage (V
OUT
).
In one embodiment a DC-to-DC conversion circuit having an input conductor receiving an input voltage (V
IN
) and an output conductor (
15
) for conducting an output voltage (V
OUT
), the DC-to-DC conversion circuit includes a pass transistor (
14
) having a first electrode coupled to receive the input voltage (V
IN
) and the second electrode coupled to the circuit node (
17
). An amplifier circuit (
13
) driving the pass transistor has a first input coupled to receive a first reference voltage (V
REF
) and second input receiving the feedback signal (
16
). A level-shifting isolation capacitor (C
LS
) is coupled between the circuit node (
17
) and the output conductor (
15
). A charge pump circuit includes a first input terminal coupled to receive a second reference voltage (GND), a second input terminal coupled to receive the input voltage (V
IN
), a first output term

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