System and method for calibrating pulse width and delay

Abstract

A system and method for calibrating a duration of a pulse or a delay. A reference clock signal includes a sequence of reference pulses, and controls a switch in a first charge pump that is configured to charge a first capacitor. Each of a sequence of test pulses controls a switch in a second charge pump that is configured to charge a second capacitor. At the end of each charging cycle, the respective capacitor voltages are compared and the duration of the test pulses is adjusted, by a feedback circuit, in a direction tending to make the capacitor voltages equal. When the capacitor voltages are equal, the ratio of the lengths of the reference pulses and test pulses equals the ratio of the capacitances, if the charge pumps deliver the same current when switched on.

What is claimed is: 
     
         1 . A system for calibrating, the system comprising:
 a first charge pump having a control input and a current output and being configured to receive a sequence of reference pulses at the control input;   a first pulse generator having a pulse width control input, and being configured to generate a sequence of test pulses, each of the test pulses having a duration controlled by a signal received at the pulse width control input; and   a feedback circuit, connected to the pulse width control input of the first pulse generator, configured to adjust, based on a test voltage and on a reference voltage, the duration of the test pulses in a direction to reduce a difference between the reference voltage and the test voltage, the test voltage being based on the test pulses.   
     
     
         2 . The system of  claim 1 , wherein the first charge pump is further configured to source or sink a current at the current output during each of the reference pulses. 
     
     
         3 . The system of  claim 1 , further comprising:
 a first capacitor, connected to the current output of the first charge pump and configured to be charged to the reference voltage during each of the reference pulses;   a second charge pump having a control input and a current output and being configured to:   receive the sequence of test pulses at the control input; and   source or sink a current at the current output during each of the test pulses;   a second capacitor, connected to the current output of the second charge pump and configured to be charged to the test voltage during each of the test pulses; and   a reset circuit configured to:   charge or discharge the first capacitor to a starting voltage before beginning of each of the reference pulses; and   charge or discharge the second capacitor to the starting voltage before beginning of each of the test pulses.   
     
     
         4 . The system of  claim 3 , wherein a capacitance of the first capacitor is the same as a capacitance of the second capacitor, and wherein a capacitance of one or more of the first capacitor and the second capacitor is adjustable during operation. 
     
     
         5 . The system of  claim 3 , wherein the feedback circuit comprises a differential amplifier having a first input connected to the first capacitor and a second input connected to the second capacitor, wherein the feedback circuit further comprises an integrator connected to an output of the differential amplifier, and to the pulse width control input of the first pulse generator. 
     
     
         6 . The system of  claim 5 , wherein the integrator comprises a capacitor, and the pulse width control input of the first pulse generator is an analog input, wherein the integrator further comprises an up-down counter, and the pulse width control input of the first pulse generator is a digital input. 
     
     
         7 . The system of  claim 1 , further comprising a second pulse generator, the second pulse generator having a pulse width control input, the feedback circuit being further connected to the pulse width control input of the second pulse generator, wherein the second pulse generator is configured to generate a sequence of slave pulses each having a width equal to a multiple of a width of a corresponding test pulse of the sequence of test pulses. 
     
     
         8 . The system of  claim 1 , wherein:
 the first pulse generator comprises:
 a circuit configured to generate a delay control signal; and 
 a first controllable delay element configured to incur a controllable delay controlled by the delay control signal, and 
   the first pulse generator is configured to generate the sequence of test pulses with each test pulse having a pulse width equal to a length of the controllable delay.   
     
     
         9 . The system of  claim 8 , further comprising a second controllable delay element configured to incur a delay controlled by the delay control signal, wherein the second controllable delay element is configured to incur a delay equal to a multiple of a delay incurred by the first controllable delay element. 
     
     
         10 . A method for calibrating, the method comprising:
 charging a first capacitor to a reference voltage, with a current of a first charge pump, during a reference pulse; and   generating a second test pulse, based on a test voltage during a first test pulse and on the reference voltage,   wherein the second test pulse being shorter or longer than the first test pulse based on a shorter test pulse or a longer test pulse reducing a difference between the test voltage and the reference voltage.   
     
     
         11 . The method of  claim 10 , further comprising:
 charging a second capacitor to the test voltage with a current of a second charge pump, during the first test pulse; and   before beginning of the reference pulse, charging or discharging the first capacitor to a starting voltage,   before beginning of the first test pulse, charging or discharging the second capacitor to the starting voltage, and   after end of the reference pulse and end of the first test pulse, comparing the test voltage and the reference voltage with a differential amplifier.   
     
     
         12 . The method of  claim 11 , wherein a capacitance of the first capacitor is the same as a capacitance of the second capacitor and wherein a capacitance of one or more of the first capacitor and the second capacitor is adjustable during operation. 
     
     
         13 . The method of  claim 10 , further comprising generating a slave pulse having a width equal to a multiple of a width of the second test pulse, wherein the slave pulse has a width equal to a width of the second test pulse. 
     
     
         14 . A system for calibrating, the system comprising:
 a first charge pump configured to receive a sequence of reference pulses;   a first capacitor connected to the first charge pump and configured to be charged to a reference voltage during each of the reference pulses;   a first pulse generator configured to generate a sequence of test pulses;   a second pulse generator configured to generate a sequence of slave pulses each having a width equal to a multiple of a width of a corresponding test pulse of the sequence of test pulses; and   a feedback circuit, connected between the first capacitor and the first pulse generator, configured to adjust, a duration of the test pulses in a direction to reduce a difference between the reference voltage and a test voltage, the test voltage being based on the test pulses, wherein the feedback circuit is further connected to the second pulse generator.   
     
     
         15 . The system of  claim 14 , wherein the first charge pump comprising a control input and a current output and configured to source or sink a current at the current output during each of the reference pulses. 
     
     
         16 . The system of  claim 14 , further comprising:
 a second charge pump having a control input and a current output and being configured to:   receive the sequence of test pulses at the control input; and   source or sink a current at the current output during each of the test pulses;   a second capacitor, connected to the current output of the second charge pump and configured to be charged to the test voltage during each of the test pulses; and   a reset circuit configured to:   charge or discharge the first capacitor to a starting voltage before beginning of each of the reference pulses; and   charge or discharge the second capacitor to the starting voltage before beginning of each of the test pulses.   
     
     
         17 . The system of  claim 16 , wherein the feedback circuit comprises a differential amplifier having a first input connected to the first capacitor and a second input connected to the second capacitor, wherein the feedback circuit further comprises an integrator connected to an output of the differential amplifier, and to a pulse width control input of the first pulse generator. 
     
     
         18 . The system of  claim 17 , wherein the integrator comprises a capacitor, and the pulse width control input of the first pulse generator is an analog input, wherein the integrator further comprises an up-down counter, and the pulse width control input of the first pulse generator is a digital input. 
     
     
         19 . The system of  claim 14 , wherein:
 the first pulse generator comprises:
 a circuit configured to generate a delay control signal; and 
 a first controllable delay element configured to incur a controllable delay controlled by the delay control signal, and 
   the first pulse generator is configured to generate the sequence of test pulses with each test pulse having a pulse width equal to a length of the controllable delay.   
     
     
         20 . The system of  claim 19 , further comprising a second controllable delay element configured to incur a delay controlled by the delay control signal, wherein the second controllable delay element is configured to incur a delay equal to a multiple of a delay incurred by the first controllable delay element.