Symmetric charge pump replica bias detector

Abstract

A charge pump replica bias detector is disclosed which provides a charge pump with a greater working output voltage range or larger output compliance. A larger working range will provide a charge pump with more symmetric source and sink currents than prior designs with a reduction of the multiple frequency sideband levels that occur in a voltage controlled oscillator of a phase-locked loop synthesizer. Further improvements are the prevention of disturbances of the loop filter voltage level due to unwanted leakage currents in a charge pump that are dependent on the value of loop filter voltage. Finally, by providing improved output voltage compliance and limiting loop filter voltage disturbances there are improvements in the reduction in reference frequency feed-through, charge sharing and noise transient coupling and phase noise in the phase-locked loop. Possible applications include but are not limited to charge pump phase-locked loop designs for single chip CMOS multi-band and multi-standard radio frequency transceiver integrated circuits.

1 . A replica bias clamp detector that maximizes a charge pump's output voltage compliance by monitoring and limiting the leakage current in a charge pump circuit comprising:
 a voltage buffer follower responsive to a charge pump circuit output voltage level and providing a voltage output and current output;   a voltage comparator whose output signal limits a circuit's leakage current by responding to an input voltage sensing level;   a constant discharging current source to establish a fixed dc input voltage level for a comparator in the absence of charge pump leakage;   an inverter circuit whose output is responsive to a sensing input voltage;   a replica pull-up current source of an existing charge pump circuit responsive to a charge pump output and providing a charging leakage current path; and   a transmission switch responsive to the bi-directional flow of a current;   
     
     
         2 . The replica bias clamp detector of  claim 1  further comprising:
 a second voltage comparator whose output signal limits a circuit's leakage current by responding to a second input voltage sensing level; 
 a constant charging current source to establish a second fixed dc input voltage level for a second comparator in the absence of charge pump leakage; 
 a second inverter circuit whose output is responsive to a second sensing input voltage; 
 a replica pull-down current source of an existing charge pump circuit responsive to a charge pump output and providing a discharge leakage current path; and 
 a second transmission switch responsive to the bi-directional flow of a current. 
 
     
     
         3 . The replica bias clamp detector  claim 1  wherein the transmission switch includes:
 a complimentary transmission gate coupled to the replica pull-up current source and a leakage detection comparator input and constant current source bias supply coupled between the transmission gate and supply. 
 
     
     
         4 . The replica bias clamp detector  claim 2  wherein the second transmission switch includes:
 a second complimentary transmission gate coupled to the replica pull-down current source and a second leakage detection comparator input and second constant current source bias supply coupled between the second transmission gate and ground. 
 
     
     
         5 . The comparator of  claim 1  whereby a constant discharging current is used to establish a fixed dc input voltage level for an inverter circuit whose output will change state responsive to an external discharge current. 
     
     
         6 . A second comparator of  claim 2  whereby a constant charging current is used to establish a fixed dc input voltage level for a second inverter circuit whose output will change state responsive to an external discharge current. 
     
     
         7 . A method of monitoring and limiting a charge pump's reverse leakage current that maximizes the charge pump's output voltage compliance using a replica bias clamp detector comprising:
 a voltage follower buffer responsive to a charge pump circuit output voltage level and providing an output voltage and output current;   a replica pull-up current source that provides a reverse leakage current responsive to a voltage follower buffer output voltage level;   a complimentary transmission gate switch coupled to the pull-up current source and a leakage detection comparator input and a pull-down constant current source bias supply coupled between the complementary transmission gate and ground;   a constant discharging current source to establish a fixed dc input voltage sensing level at the input of a comparator in the absence of charge pump leakage; and   a voltage comparator responsive to an input voltage sensing level that controls transmission switch closure in a given charge pump to limit leakage current.   
     
     
         8 . The method of  claim 6  further comprising:
 a replica pull-down current source that provides a reverse leakage current responsive to a voltage follower buffer output voltage and current levels; 
 a second complimentary transmission gate switch coupled to the pull-down current source and a second leakage detection comparator input and a pull-up constant current source bias supply coupled between the complementary transmission gate and ground; 
 a constant charging current source to establish a fixed dc input voltage sensing level at the input of a second comparator in the absence of charge pump leakage coupled between the supply; and 
 a second voltage comparator responsive to an input voltage sensing level that controls a second transmission switch closure in a given charge pump to limit leakage current. 
 
     
     
         9 . The method of  claim 6  wherein the replica pull-up current source provides;
 an accurate measure of reverse leakage current in an existing charge pump circuit. 
 
     
     
         10 . The method of  claim 6  wherein the unity gain voltage buffer source provides;
 an accurate measure of reverse leakage current in existing charge pump circuit to a transmission switch coupled to the pull-up current source and a second leakage detection comparator input and a pull-down constant current source bias supply coupled between the complementary transmission gate and ground. 
 
     
     
         11 . The method of  claim 7  wherein the replica pull-down current source provides;
 an accurate measure of reverse leakage current in an existing charge pump circuit. 
 
     
     
         12 . The method of  claim 7  wherein the unity gain voltage buffer source provides;
 an accurate measure of reverse leakage current in existing charge pump circuit to a second transmission switch coupled to the pull-down current source and a second leakage detection comparator input and a pull-up constant current source bias supply coupled between the complementary transmission gate and ground.