Apparatus and method for phase lock loop gain control using unit current sources
CAFCFirst Claim
1. A gain compensator circuit that determines a reference pump current for a charge pump in a phase lock loop (PLL), comprising:
- a plurality of unit current sources that are arranged into at least one group, said group responsive to a capacitor control signal and generating a portion of the reference pump current when said group is activated, wherein said capacitor control signal also controls a corresponding fixed capacitor; and
means for simultaneously scaling said unit current sources responsive to a PLL control signal that is representative of at least one of a reference frequency, a loop bandwidth, and a damping factor of said PLL.
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Abstract
A gain compensator compensates for the gain variation of a varactor-tuned voltage tuned oscillator (VCO) in a phase lock loop (PLL). The VCO includes a parallel LC circuit having multiple fixed capacitors that can be switched-in or switched-out of the LC circuit according to a capacitor control signal to perform band-select tuning of the VCO. The gain compensator compensates for the variable VCO gain by generating a charge pump reference current that is based on the same capacitor control signal that controls the fixed capacitors in the LC circuit. The gain compensator generates the charge pump reference current by replicating a reference scale current using unit current sources. The number of times the reference scale current is replicated is based on the fixed capacitance that is switched-in to the LC circuit and therefore the frequency band of the PLL. The reference scale current is generated based on a PLL control that specifics certain PLL characteristics such as reference frequency, loop bandwidth, and loop damping. Therefore, the reference pump current can be efficiently optimized for changing PLL operating conditions, in addition to compensating for variable VCO gain.
151 Citations
39 Claims
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1. A gain compensator circuit that determines a reference pump current for a charge pump in a phase lock loop (PLL), comprising:
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a plurality of unit current sources that are arranged into at least one group, said group responsive to a capacitor control signal and generating a portion of the reference pump current when said group is activated, wherein said capacitor control signal also controls a corresponding fixed capacitor; and
means for simultaneously scaling said unit current sources responsive to a PLL control signal that is representative of at least one of a reference frequency, a loop bandwidth, and a damping factor of said PLL. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
a switch that is connected to said group of unit current sources, wherein said switch applies said gate voltage to said group of unit current sources when said corresponding fixed capacitor is switched-in to a resonant circuit.
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14. A gain compensator circuit that determines a reference pump current for a charge pump in a phase lock loop (PLL), comprising:
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a plurality of unit current sources that are arranged into at least one group, said group generating a portion of the reference pump current when said group is activated;
a voltage generator that generates a gate voltage based on a PLL control signal; and
a switch that is connected to said group of unit current sources, wherein said switch is controlled by a corresponding capacitor control signal that also controls a fixed capacitor in a VCO tuning circuit, wherein said switch connects said gate voltage to said corresponding group of unit current sources according to said capacitor control signal;
wherein said voltage generator includes a current scaler that generates a reference scale current according to a PLL control signal, and means for generating said gate voltage based on said reference scale current. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. A method of compensating the gain of a phase lock loop (PLL), comprising the steps of:
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(1) generating a reference scale current;
(2) switching a fixed capacitor into a VCO tuning circuit that is part of a VCO to tune a frequency of said VCO;
(3) replicating said reference scale current a number of times when said fixed capacitor is switched-in to said VCO tuning circuit, wherein the number of times said reference scale current is replicated is based on said fixed capacitor;
(4) contributing said replicated currents to a reference charge pump current for said PLL; and
(5) adjusting said reference scale current based on a PLL control signal that indicates characteristics of said PLL. - View Dependent Claims (22, 23)
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24. A method of compensating the gain of a phase lock loop (PLL), comprising the steps of:
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(1) receiving at least one capacitor control signal that controls a corresponding fixed capacitor in a VCO tuning circuit;
(2) generating a reference scale current;
(3) activating a group of unit current sources based on said capacitor control signal;
(4) replicating said reference scale current a number of times in said activated group, wherein said number of times said reference scale current is replicated is based on said fixed capacitor that is controlled by said capacitor control signal;
(5) summing together said replicated currents to form a reference charge pump current for said PLL; and
(6) adjusting said reference scale current based on a PLL control signal that is representative of characteristics of the PLL, and thereby simultaneously adjusting said replicated currents that form said reference pump current according to said characteristics of the PLL. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31)
(7) de-activating said group of unit current sources based on said capacitor control signal.
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30. The method of claim 24, further comprising the step of
(7) de-activating said group of unit current sources when said corresponding fixed capacitor is switched-out of said VCO tuning circuit by said capacitor control signal. -
31. The method of claim 30, wherein each of said unit current sources is a field effect transistor (FET), and wherein said step of de-activating comprises the step of cutting-off said FETs in said de-activated group.
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32. A gain compensator circuit that determines a reference pump current for a charge pump in a phase lock loop (PLL), comprising:
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a plurality of unit current sources that are arranged into at least one group, said group responsive to a capacitor control signal and generating a portion of the reference pump current when said group is activated, wherein said capacitor control signal also controls a corresponding fixed capacitor of a voltage controlled oscillator (VCO) in the PLL; and
means for simultaneously scaling said unit current sources responsive to a PLL control signal that is representative of a characteristic of the PLL
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33. A gain compensator circuit that determines a reference pump current for a charge pump in a phase lock loop (PLL), comprising
a plurality of unit current sources that are arranged into at least one group, said group responsive to a capacitor control signal and generating a portion of the reference pump current when said group is activated, wherein said capacitor control signal also controls a corresponding fixed capacitor of a voltage controlled oscillator (VCO) in the PLL; - and
a current mirror including one or more weighted current sources that generate a reference scale current responsive to a PLL control signal, the PLL control signal representative of one or more characteristics of the PLL, each of said unit current sources generating a unit current proportional to said reference scale current, said unit currents summed together to form the reference pump current. - View Dependent Claims (34, 35, 36, 37, 38, 39)
a switch that is connected to said group of unit current sources, wherein said switch applies said gate voltage to said group of unit current sources when said corresponding fixed capacitor is switched-in to said VCO.
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Specification