Calibration of offset gain and phase errors in M-channel time-interleaved analog-to-digital converters

Abstract

Techniques for correcting component mismatches in an M-channel time-interleaved Analog to Digital Converter (ADC). In order to obtain an error measure for offset, gain or phase, errors, outputs from each ADC are either summed or averaged over N o samples. Calling each of the sums or averages as X k where k=1, 2, . . . , M, there are M such values as a result. A single value representing the mean of these M values, X mean , is chosen as a reference value. The offset, gain and phase errors for the M different ADCs are then obtained from X k −X mean . The sign of each offset error, i.e., sign (X k −X mean ), is then used to drive an adaptive algorithm whose output represents an offset correction value for the corresponding ADC. The offset, gain, and phase correction outputs from the adaptive algorithm is fed to an array of Digital-to-Analog converters (DACs) whose outputs are voltages or currents that directly or indirectly controls the offset, gain or phase setting of each individual ADC. Thus, there are M different offset, gain and phase error signals and M different adaptive algorithms operating in conjunction with M different DACs providing offset control signals to M different ADCs. In certain embodiments, spur frequencies can be reduced with the use of notch filters.

What is claimed is: 
     
       1. An apparatus comprising:
 a clock signal generator, for generating a plurality, M, of clock signals at a frequency f and a period T; each of the M clock signals having a different one of a selected plurality, M, of clock phases 
 a plurality, M, of Analog to Digital Converters (ADCs) coupled to the clock signal generator, the ADCs for converting an input signal to a set of ADC outputs as M digital values in response to a respective one of the M clock signals, each of the ADCs having an offset correction input, a gain correction input, and a phase correction input; 
 an adaptive processor, coupled to receive the M digital values, the adaptive processor estimating one or more correction signals for at least one of offset, gain, and phase error in at least one of the MADCs, the adaptive processor determining the correction signals by:
 determining M accumulated values, X k , for k=1 to M, by individual accumulation of the M digital values over a predetermined number of ADC output samples; 
 determining a reference value, X mean , from a combination of the M accumulated values; 
 providing an adjusted set of set of digital values, E offset k, for k=1 to M, from the M accumulated values, X k , and the reference value X mean ; 
 from the adjusted set of digital values, determining at least one of an offset, gain and phase correction value corresponding to one or more estimated correction signals to be applied to correct at least one of offset, gain, and phase error of at least one of the ADCs; 
 the estimated correction signals connected to at least one of the offset, gain, and/or correction inputs of the ADCs; and 
 a multiplexer, for interleaving the M digital values output by the ADCs to form a digital representation of the input signal. 
 
 
     
     
       2. The apparatus of  claim 1  additionally comprising: one or more notch filters, coupled to the ADCs, to filter spur frequency content in the M digital values resulting from at least one of the gain or phase error. 
     
     
       3. The apparatus of  claim 1  wherein the adaptive processor further determines the offset correction values by determining an accumulated offset for each of the plurality, M, of ADCs. 
     
     
       4. The apparatus of  claim 1  wherein the adaptive processor further determines the gain correction value by determining an accumulated gain error for each of the plurality, M, of ADCs. 
     
     
       5. The apparatus of  claim 1  wherein the adaptive processor further determines the phase correction value by determining an accumulated phase error for each of the plurality of ADCs. 
     
     
       6. The apparatus of  claim 1  wherein the adaptive processor sequentially determines the offset, gain, and phase correction values. 
     
     
       7. The apparatus of  claim 1  further including a pluralality of digital-to-analog converters (DACs), where each DAC converts at least one of an offset, gain, or phase correction value to an analog signal input to at least one of the offset, gain, or phase inputs to the plurality, M, of ADCs. 
     
     
       8. The apparatus of  claim 1  further including additional adaptive processors, the adaptive processors configured to process offset, gain, and phase correction values in parallel. 
     
     
       9. The apparatus of  claim 1  wherein the adaptive processor further determines the offset correction value and further comprising:
 a signum block for determining a sign of the offset error; 
 a multiplier for multiplying the output of the signum block by an step size; 
 a feedback loop for summing and delaying an output of the multiplier; 
 a rounding block for rounding an output of the feedback loop; and 
 an offset biasing block for biasing the output of the rounding block by an offset bias amount. 
 
     
     
       10. The apparatus of  claim 1  wherein the adaptive processor further determines the gain correction value and further comprises:
 a signum block for determining a sign of the gain error; 
 a multiplier for multiplying the output of the signum block by an gain step size; 
 a feedback loop for summing and delaying an output of the multiplier; 
 a rounding block for rounding an output of the feedback loop; and 
 a gain biasing block for biasing the output of the rounding block by a gain bias amount. 
 
     
     
       11. The apparatus of  claim 1  wherein the adaptive processor further determines the phase correction value and further comprises:
 a signum block for determining a sign of the phase error; 
 a multiplier for multiplying the output of the signum block by a phase step size; 
 a feedback loop for summing and delaying an output of the multiplier; 
 a rounding block for rounding an output of the feedback loop; and 
 a phase biasing block for biasing the output of the phase rounding block by a phase bias amount. 
 
     
     
       12. The apparatus of  claim 1  additionally comprising:
 a receiver, for receiving the input signal from a communication system. 
 
     
     
       13. The apparatus of  claim 1  additionally comprising:
 a diplexer, coupled to receive a cable signal from a cable network, and to provide a received cable signal; 
 a variable gain amplifier, for amplifying the received cable signal and to provide an amplified cable signal; and 
 a filter, connected to filter the amplified cable signal to provide the input signal to the plurality, M, of ADCs. 
 
     
     
       14. A method comprising the steps of:
 generating a plurality, M, of clock signals at a frequency f and a period T; each of the M clock signals having a different one of a selected plurality, M, of clock phases; 
 convertering an input analog signal to M digital signals via M individual ADC operations, to generate a set of ADC outputs as M digital values each in response to a respective one of the M clock signals, each of the M ADC operations having an offset correction input, a gain correction input, and a phase correction input; 
 estimating one or more correction signals for at least one of offset, gain, and phase error in at least one of the MADC operations, via the further steps of:
 determining M accumulated values, Xk, for k=1 to M, by individual accumulation of the M digital values over a predetermined number of ADC operation output samples; 
 determining a reference value, Xmean, from a combination of the M accumulated values; 
 providing an adjusted set of set of digital values, Eoffsetk, for k=1 to M, from the M accumulated values, Xk, and the reference value Xmean; 
 from the adjusted set of digital values, determining at least one of an offset, gain and phase correction value corresponding to one or more estimated correction signals to be applied to correct at least one of offset, gain, and phase error of at least one of the ADC operations; 
 coupling the estimated correction signals to at least one of the offset, gain, and/or correction inputs of the individual ADC operations; and 
 interleaving the M digital values output by the ADCs to form a digital representation of the input signal. 
 
 
     
     
       15. The method of  claim 14  additionally comprising:
 applying one or more notch filter operations to the outputs of the ADCs, to filter spur frequency content in the M digital values resulting from at least one of the gain or phase error. 
 
     
     
       16. The method of  claim 14  further comprising:
 determining the offset correction values by determining an accumulated offset for each of the plurality, M, of ADCs. 
 
     
     
       17. The method of  claim 14  further comprising:
 determining the gain correction value by determining an accumulated gain error for each of the plurality of ADCs. 
 
     
     
       18. The method of  claim 14  further comprising:
 determining the phase correction value by determining an accumulated phase error for each of the plurality of ADCs. 
 
     
     
       19. The method of  claim 14  further comprising;
 sequentially determining the offset, gain, and phase correction values. 
 
     
     
       20. The method of  claim 14  further comprising:
 Digital to Analog converting at least one of an offset, gain, or phase correction value to one or more analog input signals; and 
 coupling the analog input signals to at least one of the offset, gain, or phase inputs of the plurality, M, of ADCs. 
 
     
     
       21. The method of  claim 14  further comprising:
 processing the offset, gain, and phase correction values in parallel. 
 
     
     
       22. The method of  claim 14  further comprising:
 determining a sign of the offset error; 
 multiplying the output of the signum block by an step size; 
 summing and delaying an output of the multiplier; 
 rounding an output of the feedback loop; and 
 biasing the output of the rounding block by an offset bias amount. 
 
     
     
       23. The method of  claim 14  further comprising:
 determining a sign of the gain error; 
 multiplying the output of the signum block by an gain step size; 
 summing and delaying an output of the multiplier; 
 rounding an output of the feedback loop; and 
 biasing the output of the rounding block by a gain bias amount. 
 
     
     
       24. The method of  claim 14  further comprising:
 determining a sign of the phase error; 
 multiplying the output of the signum block by a phase step size; 
 summing and delaying an output of the multiplier; 
 rounding an output of the feedback loop; and 
 biasing the output of the phase rounding block by a phase bias amount. 
 
     
     
       25. The method of  claim 14  additionally comprising:
 receiving the input signal from a communication system. 
 
     
     
       26. The method of  claim 14  additionally comprising:
 receiving a cable signal from a cable network, to provide a received cable signal; 
 amplifying the received cable signal to provide an amplified cable signal; and 
 filtering the amplified cable signal to provide the input signal to the plurality, M, of ADCs. 
 
     
     
       27. An apparatus comprising:
 a plurality of Analog to Digital Converters (ADCs) coupled to receive one or more clock signals, the ADCs arranged to convert an input signal to a set of ADC outputs as digital values, each of the ADCs having at least one of an offset correction input, a gain correction input, or a phase correction input;   a processor, coupled to receive the set of digital values, the processor estimating one or more correction signals for at least one of offset, gain, or phase error in at least one of the ADCs, the adaptive processor further to:
 accumulate a plurality of the digital values provided by the ADCs to produce accumulated values; 
 determine a reference value from a combination of the accumulated values; 
 provide an adjusted set of set of digital values from the accumulated values and the reference value; 
 from the adjusted set of digital values, determine at least one of an offset, gain or phase correction value corresponding to one or more estimated correction signals to be applied to correct at least one of offset, gain, and phase error input of at least one of the ADCs; 
   a circuit, for coupling the estimated correction signals to at least one of the offset, gain, and/or correction inputs of at least one of the ADCs; and   a multiplexer, for interleaving the digital values output by the ADCs to form a digital representation of the input signal.   
     
     
       28. The apparatus of claim 27 additionally comprising:
 one or more notch filters, coupled to the ADCs, to filter frequency content in the digital values resulting from at least one of the gain or phase error.   
     
     
       29. The apparatus of claim 27 wherein the processor is further to determine the offset correction values via an accumulated offset for each of the plurality of ADCs. 
     
     
       30. The apparatus of claim 27 wherein the processor is further to determine the gain correction value by determining an accumulated gain error for each of the plurality of ADCs. 
     
     
       31. The apparatus of claim 27 wherein the processor is further to determine the phase correction value via an accumulated phase error for each of the plurality of ADCs. 
     
     
       32. The apparatus of claim 27 wherein the processor sequentially determines the offset, gain, and phase correction values. 
     
     
       33. The apparatus of claim 27 wherein the circuit further comprises a plurality of digital-to-analog converters (DACs), where each DAC converts at least one of an offset, gain, or phase correction value to an analog signal input to at correct least one of the offset, gain, or phase inputs to the plurality of ADCs. 
     
     
       34. The apparatus of claim 27 further including additional processors, the additional processors configured to provide offset, gain, and phase correction values in parallel to the respective offset, gain, and phase correction inputs to the ADCs. 
     
     
       35. The apparatus of claim 27 wherein the processor further determines the offset correction value and further comprising:
 a signum block for determining a sign of the offset error;   a multiplier for multiplying the output of the signum block by an step size;   a feedback loop for summing and delaying an output of the multiplier;   a rounding block for rounding an output of the feedback loop; and   an offset biasing block for biasing the output of the rounding block by an offset bias amount.   
     
     
       36. The apparatus of claim 27 wherein the processor further determines the gain correction value and further comprises:
 a signum block for determining a sign of the gain error;   a multiplier for multiplying the output of the signum block by an gain step size;   a feedback loop for summing and delaying an output of the multiplier;   a rounding block for rounding an output of the feedback loop; and   a gain biasing block for biasing the output of the rounding block by a gain bias amount.   
     
     
       37. The apparatus of claim 27 wherein the processor further determines the phase correction value and further comprises:
 a signum block for determining a sign of the phase error;   a multiplier for multiplying the output of the signum block by a phase step size;   a feedback loop for summing and delaying an output of the multiplier;   a rounding block for rounding an output of the feedback loop; and   a phase biasing block for biasing the output of the phase rounding block by a phase bias amount.   
     
     
       38. The apparatus of claim 27 additionally comprising:
 a receiver, for receiving the input signal from a communication system.   
     
     
       39. The apparatus of claim 27 additionally comprising:
 a diplexer, coupled to receive a cable signal from a cable network, and to provide a received cable signal;   a variable gain amplifier, for amplifying the received cable signal and to provide an amplified cable signal; and   a filter, connected to filter the amplified cable signal to provide the input signal to the plurality of ADCs.   
     
     
       40. A method comprising the steps of:
 converting an input analog signal using a plurality of individual ADC operations, to generate a set of sampled digital values, each of the individual ADC operations having at least one of an offset correction input, a gain correction input, or a phase correction input;   estimating one or more correction signals for at least one of offset, gain, and phase error in at least one of the individual operations, via the further steps of:
 accumulating the digital values over time, to provide accumulated values; 
 determining a reference value from a combination of the accumulated values; 
 providing an adjusted set of set of digital values from the accumulated values and the reference value; 
 from the adjusted set of digital values, determining at least one of an offset, gain or phase correction value corresponding to one or more estimated correction signals to be applied to correct at least one of offset, gain, or phase error of at least one of the ADC operations; 
 coupling the estimated correction signals to at least one offset, gain, or phase correction input of the at least one of the individual operations; and 
 multiplexing the first and second digital signal, to form a digital representation of the input signal. 
   
     
     
       41. The method of claim 40 additionally comprising:
 applying one or more notch filter operations to the outputs of the individual operations, to filter frequency content in the digital values resulting from at least one of the gain or phase error.   
     
     
       42. The method of claim 40 further comprising:
 determining the offset correction value by determining an accumulated offset for each of the plurality of operations.   
     
     
       43. The method of claim 40 further comprising:
 determining the gain correction value by determining an accumulated gain error for each of the plurality of operations.   
     
     
       44. The method of claim 40 further comprising:
 determining the phase correction value by determining an accumulated phase error for each of the plurality of operations.   
     
     
       45. The method of claim 40 further comprising:
 sequentially determining the offset, gain, and phase correction values.   
     
     
       46. The method of claim 40 wherein the coupling step further comprises:
 Digital to Analog converting at least one of an offset, gain, or phase correction value to one or more analog input signals; and   coupling the analog input signals to at least one of the offset, gain, or phase inputs.   
     
     
       47. The method of claim 40 further comprising:
 determining each of the offset, gain, and phase correction values in parallel.   
     
     
       48. The method of claim 42 further comprising:
 determining a sign of the offset error;   multiplying the sign by a step size; and   summing and delaying a result of the multiplying step.   
     
     
       49. The method of claim 43 further comprising:
 determining a sign of the gain error;   multiplying the sign by a gain step size;   summing and delaying a result of the multiplying step;   rounding a result of the summing and delaying; and   biasing a result of the rounding by a gain bias amount.   
     
     
       50. The method of claim 44 further comprising:
 determining a sign of the phase error;   multiplying the sign by a phase step size;   summing and delaying a result of the multiplying step;   rounding a result of the summing and delaying; and   biasing a result of the phase rounding by a phase bias amount.   
     
     
       51. The method of claim 40 additionally comprising:
 receiving the input signal from a communication system.   
     
     
       52. The method of claim 40 additionally comprising:
 receiving a cable signal from a cable network, to provide a received cable signal;   amplifying the received cable signal to provide an amplified cable signal: and   filtering the amplified cable signal to provide the input signal.