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US5646563A
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Charge pump with near zero offset current
Assignee: National Semiconductor Corp
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Filing: 1996-09-30
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Granted: 1997-07-08
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Expires: 2016-09-30
Abstract
Abstract A charge pump of a phase-locked loop includes a first P channel transistor and a first N channel transistor coupled to mirror a current in a constant current source. The P channel transistor and N channel transistor are formed with dimensions that match transient responses of currents through the N and P channel transistors during switching rather than matching the gains of the N and P channel transistors. In one embodiment, the channel length of the N channel transistor is twice a channel length of the P channel transistor. A second P channel transistor and a second N channel transistor connected in series with the first P and N channel transistors switch the current through the first P channel transistor and the first N channel transistor respectively. The second P channel transistor and the second N channel transistor have matched gate-drain capacitances so that they have the same switching speed. A first capacitor coupled between the gate of the first P channel transistor and a supply voltage and a second capacitor coupled between the gate of the first N channel transistor and a reference voltage reduce the effect that jitter in the supply and reference voltages has on the charge pump.
Inventors
- 👤 James R. Kuo
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 16:08
CPC Classifications
H; H03; H03L; H03L7/00; H03L7/06; H03L7/08; H03L7/085; H03L7/089; H03L7/0891; H03L7/0895
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
240 words
A charge pump comprising: a constant current source; a P channel transistor having a gate coupled to the constant current source so that a current through the P channel transistor mirrors a current of the constant current source; an N channel transistor having a gate coupled to the constant current source so that a current through the N channel transistor mirrors the current of the constant current source, wherein the P channel transistor and the N channel transistor are connected in series between a first voltage terminal and a second voltage terminal; a first switching transistor connected in series with the P channel transistor, wherein a voltage applied to a gate of the first switching transistor controls whether current through the P channel transistor flows to a capacitive node between the P channel transistor and the N channel transistor; and a second switching transistor connected in series with the N channel transistor, wherein a voltage applied to a gate of the second switching transistor controls whether current through the N channel transistor flows from the capacitive node, wherein a difference between a dimension of the P channel transistor and a corresponding dimension of the N channel transistor equalizes transient responses that occur in the current through the P channel transistor and in the current through the N channel transistor when the first and second switching transistors turn on the currents through the P channel transistor and the N channel transistor.
Claim 2
Dependent Claim
240 words
A charge pump comprising: a constant current source; a P channel transistor having a gate coupled to the constant current source so that a current through the P channel transistor mirrors a current of the constant current source; an N channel transistor having a gate coupled to the constant current source so that a current through the N channel transistor mirrors the current of the constant current source, wherein the P channel transistor and the N channel transistor are connected in series between a first voltage terminal and a second voltage terminal; a first switching transistor connected in series with the P channel transistor, wherein a voltage applied to a gate of the first switching transistor controls whether current through the P channel transistor flows to a capacitive node between the P channel transistor and the N channel transistor; and a second switching transistor connected in series with the N channel transistor, wherein a voltage applied to a gate of the second switching transistor controls whether current through the N channel transistor flows from the capacitive node, wherein a difference between a dimension of the P channel transistor and a corresponding dimension of the N channel transistor equalizes transient responses that occur in the current through the P channel transistor and in the current through the N channel transistor when the first and second switching transistors turn on the currents through the P channel transistor and the N channel transistor.
Claim 3
Dependent Claim
15 words
The charge pump of claim 1, further comprising a filter coupled to the capacitive node.
Claim 4
Dependent Claim
25 words
The charge pump of claim 1, wherein the first switching transistor has a gate-drain capacitance equal to a gate-drain capacitance of the second switching transistor.
Claim 5
Dependent Claim
29 words
The charge pump of claim 3, wherein a channel length of the N channel transistor is between 1.5 and 2 times a channel length of the P channel transistor.
Claim 6
Dependent Claim
25 words
The charge pump of claim 3, further comprising a first capacitor coupled between the gate of the P channel transistor and the first voltage terminal.
Claim 7
Dependent Claim
27 words
The charge pump of claim 5, wherein the first capacitor comprises a second P channel transistor having a smaller threshold voltage than the first-mentioned P channel transistor.
Claim 8
Dependent Claim
25 words
The charge pump of claim 5, further comprising a second capacitor coupled between the gate of the N channel transistor and the second voltage terminal.
Claim 9
Dependent Claim
27 words
The charge pump of claim 7, wherein the second capacitor comprises a second N channel transistor having a smaller threshold voltage than the first-mentioned N channel transistor.
Claim 10
Dependent Claim
43 words
The charge pump of claim 1, wherein the N channel transistor and the P channel transistor have equal channel widths, and a channel length of the N channel transistor is between 1.5 and 2 times a channel length of the P channel transistor.
Claim 11
Dependent Claim
25 words
The charge pump of claim 1, further comprising a first capacitor coupled between the gate of the P channel transistor and the first voltage terminal.
Claim 12
Dependent Claim
25 words
The charge pump of claim 10, further comprising a second capacitor coupled between the gate of the N channel transistor and the second voltage terminal.
Claim 13
Dependent Claim
213 words
A phase-locked loop, comprising: a voltage controlled oscillator; a phase comparator; means for connecting the voltage controlled oscillator to the phase comparator; and a charge pump comprising: a constant current source; and a first P channel transistor, a second P channel transistor, a first N channel transistor, and a second N channel transistor coupled in series between first and second voltage terminals, wherein: the first P channel transistor has a gate coupled to the constant current source so that a first current through the first P channel transistor mirrors a second current of the constant current source; a gate of the second P channel transistor is coupled to the phase comparator; the first N channel transistor has a gate coupled to the constant current source so that a third current through the first N channel transistor mirrors the second current of the constant current source; a gate of the second N channel transistor is coupled to the phase comparator; a difference between a dimension of the first P channel transistor and a corresponding dimension of the first N channel transistor equalizes transient responses in the first and third currents; and wherein the voltage controlled oscillator is coupled to a capacitive node between the first P channel transistor and the first N channel transistor.
Claim 14
Dependent Claim
213 words
A phase-locked loop, comprising: a voltage controlled oscillator; a phase comparator; means for connecting the voltage controlled oscillator to the phase comparator; and a charge pump comprising: a constant current source; and a first P channel transistor, a second P channel transistor, a first N channel transistor, and a second N channel transistor coupled in series between first and second voltage terminals, wherein: the first P channel transistor has a gate coupled to the constant current source so that a first current through the first P channel transistor mirrors a second current of the constant current source; a gate of the second P channel transistor is coupled to the phase comparator; the first N channel transistor has a gate coupled to the constant current source so that a third current through the first N channel transistor mirrors the second current of the constant current source; a gate of the second N channel transistor is coupled to the phase comparator; a difference between a dimension of the first P channel transistor and a corresponding dimension of the first N channel transistor equalizes transient responses in the first and third currents; and wherein the voltage controlled oscillator is coupled to a capacitive node between the first P channel transistor and the first N channel transistor.
Claim 15
Dependent Claim
30 words
The phase-lock loop of claim 12, wherein the charge pump further comprises a first capacitor coupled between the gate of the first P channel transistor and the first voltage terminal.
Claim 16
Dependent Claim
30 words
The phase-lock loop of claim 13, wherein the charge pump further comprises a second capacitor coupled between the gate of the first N channel transistor and the second voltage terminal.
Claim 17
Dependent Claim
26 words
The charge pump of claim 3, wherein the first switching transistor is a P channel transistors and the second switching transistor is an N channel transistor.
Claim 18
Dependent Claim
70 words
The charge pump of claim 1, wherein the difference between the dimension of the P channel transistor and the corresponding dimension of the N channel transistor equalizes transient responses that occur in the current through the P channel transistor and in the current through the N channel transistor when the first and second switching transistors simultaneously turn on the currents through the P channel transistor and the N channel transistor.
Claim 19
Dependent Claim
81 words
The phase-locked loop of claim 12, wherein when the voltage controlled oscillator provides to the phase comparator a signal having a desired frequency the phase comparator simultaneously turns on the second P channel transistor and the second N channel transistor, and wherein the difference between the dimension of the first P channel transistor and the corresponding dimension of the first N channel transistor equalizes transient responses in the first and third currents and maintains a constant voltage at the capacitive node.
References Cited (Backward Citations)
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