US 5,294,926 AGranted

Timing and amplitude error estimation for time-interleaved analog-to-digital converters

AssigneeHewlett-Packard Company

InventorJohn J. Corcoran

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Abstract

Methods for calibrating a plurality of N time-interleaved analog-to-digital converters (ADCs) for any integer N.gtoreq.2 by detecting and/or correcting timing and amplitude errors therein, where each of the ADCs, numbered j=1, 2, . . . , N has an identical clock frequency f.sub.c and period T.sub.c =(f.sub.c).sup.-1. Ideally, the N ADCs are clocked uniformly in time so that two consecutively clocked ADCs number j1 and j1+1 have effective sampling times that differ by time intervals of uniform length .DELTA.t=T.sub.c /N. Ideally, the N ADCs also have identical gains from their analog input signals to their digital output signals. In a calibration procedure, all ADCs receive a common analog input signal S.sub.in (t)=Asin[2 .pi.(1+s)f.sub.c t], where s is a non-zero fractional number satisfying -0.5<s<0.5. The output signal values from ADC number j provide a set of ordered pairs of values (t.sub.i, D.sub.ij) for sampling times t.sub.i, and the set of values {D.sub.ij }.sub.i with j fixed is approximated by another set of values { V.sub.ij =A.sub.j sin[2 .pi.sf.sub.c t.sub.i +.phi..sub.j ]}.sub.i. Here, the amplitudes A.sub.j and phase angles .phi..sub.j are chosen to provide a best numerical fit to the set {D.sub.ij }.sub.i for each j=1, 2, . . . , N, according to some criterion. The phase differences .DELTA..phi..sub.j2,j1 =.phi..sub.j2 -.phi..sub.j1 are then determined and compared with the ideal phase difference value .DELTA..PHI..sub.j2,j1 =2 .pi.(j2-j1)/N to determine if a relative timing error exists between ADCs number j1 and j2. In a similar manner, the amplitude differences A.sub.j2 -A.sub.j1 are compared to determine if a relative gain error exists between ADCs number j1 and j2.

Claims17

Dependent claims

A method for calibrating a plurality of J analog-to-digital converters for any integer J.gtoreq.2, the method comprising the steps of:

providing J analog-to-digital converters, numbered j=1, 2, . . . , J, each converter having the same clock frequency f.sub.c and period T.sub.c =1/f.sub.c and having an input terminal, a clock input terminal and an output terminal, with analog-to-digital converter number j receiving clock pulse sequence number j at the clock input terminal thereof and each clock pulse sequence having an independently adjustable time delay;
generating a sinusoidal input signal of frequency f.sub.in =(R+s)f.sub.c, where s is a non-zero fractional number satisfying -0.5<s<0.5 and R is a positive integer, and delivering this input signal to the input terminal of each of the converters;
for a predetermined time interval that includes at least 1/.vertline.s.vertline. consecutive clock pulses from each clock pulse sequence numbered j=1, 2, . . . , J, storing a sequence of output signal values, denoted D.sub.ij (i=1, 2, . . . , K), appearing at the output terminal of converter number j, where K is a positive integer satisfying K.gtoreq.1/.vertline.s.vertline., and storing a time index t.sub.i =iT.sub.c associated with each value D.sub.ij ;
expressing each set of ordered pairs {t.sub.i, D.sub.ij }.sub.i, with j fixed, approximately as a sine wave V.sub.j (t)=A.sub.j sin[2.pi.sf.sub.c t+.phi..sub.j ], and determining an amplitude A.sub.j and a phase angle .phi..sub.j associated with converter number j for the set of values {t.sub.i, D.sub.ij }.sub.i ;
and
comparing the phase differences .DELTA..phi..sub.j2,j1 =.phi..sub.j2 -.phi..sub.j1 for 1.ltoreq.j1<j2.ltoreq.J with a corresponding desired phase difference number .DELTA..PHI..sub.j2,j1 =2.pi.R(j2-j1)/J and, when the absolute difference .vertline..DELTA..PHI..sub.j2,j1 -.DELTA..phi..sub.j2,j1 .vertline. is larger than a selected positive phase angle error number .DELTA..PHI., determining that at least one of the converters number j1 and j2 has a phase err and
when a phase error occurs in at least one of the converters number j1 and j2, adjusting a time delay of at least one clock pulse sequence so that the absolute difference .vertline..DELTA..PHI..sub.j2,j1 -.DELTA..phi..sub.j2,j1 .vertline. is no greater than .DELTA..PHI..

4 more elements

A method for calibrating a plurality of J analog-to-digital converters for any integer J.gtoreq.2, the method comprising the steps of:

providing J analog-to-digital converters, numbered j=1, 2, . . . , J, each converter having the same frequency f.sub.c and period T.sub.c =1/f.sub.c and having an input terminal, a clock input terminal and an output terminal, with analog-to-digital converter number j receiving clock pulse sequence number j at the clock input terminal thereof, with each converter allowing an adjustment of amplitude of the output signal of the converter;
generating a sinusoidal input signal of frequency f.sub.in =(R+s)f.sub.c, where s is a fractional number satisfying -0.5<s<0.5, s.noteq.0, and R is a positive integer, and delivering this input signal to the input terminal of each of the converters;
for a predetermined time interval that includes at least 1/.vertline.s.vertline. consecutive clock pulses from each clock pulse sequence numbered j=1, 2, . . . , J, storing a sequence of output signal values, denoted D.sub.ij (i=1, 2, . . . , K), appearing at the output terminal of converter number j, where K is a positive integer satisfying K>1/.vertline.s.vertline., and storing a time index t.sub.i =iT.sub.c associated with each value D.sub.ij ;
expressing each set of ordered pairs {t.sub.i, D.sub.ij }.sub.i, with j fixed, approximately as a sine wave V.sub.j (t)=A.sub.j sin [2 .pi.s f.sub.c t+.phi..sub.j ], and determining an amplitude A.sub.j and a phase angle .phi..sub.j associated with converter number j for the set of values {t.sub.i, D.sub.ij }.sub.i ;
and
determining the amplitude differences .DELTA.A.sub.j2,j1 =A.sub.j2 -A.sub.j1 for 1.ltoreq.j1<j2.ltoreq.J and, when the absolute difference of at least one of these amplitude differences is larger than a selected positive amplitude number .DELTA.A, determining that at least one of the converters number j1 and j2 has an amplitude error;
and
when an amplitude error occurs in at least one of the converters number j1 and j2, adjusting an output signal amplitude of at least one of the converters so that the amplitude difference magnitude .vertline..DELTA.A.sub.j2,j1 .vertline. is no greater than .DELTA.A.

5 more elements

A method for calibrating a plurality of J analog-to-digital converters for any integer J.gtoreq.2, the method comprising the steps of:

providing J analog-to-digital converters, numbered j=1, 2, . . . , J, each converter having the same frequency f.sub.c and period T.sub.c =1/f.sub.c and having an input terminal, a clock input terminal and an output terminal, with analog-to-digital converter number j receiving clock pulse sequence number j at the clock input terminal thereof, with each clock pulse sequence having an independently adjustable time delay, and with each converter allowing an adjustment of amplitude of the output signal of the converter;
generating a sinusoidal input signal of frequency f.sub.in =(R+s)f.sub.c, where s is a non-zero fractional number satisfying -0.5<s<0.5 and R is a non-zero integer, and delivering this input signal to the input terminal of each of the converters;
for a predetermined time interval that includes at least 1/.vertline.s.vertline. consecutive clock pulses from each clock pulse sequence numbered j=1, 2, . . . , J, storing a sequence of output signal values, denoted D.sub.ij (i=1, 2, . . . , K) with j fixed, appearing at the output terminal of converter number j, where K is a positive integer satisfying K>1/.vertline.s.vertline., and storing a time index t.sub.i =iT.sub.c associated with each value D.sub.ij ;
expressing each set of ordered pairs {t.sub.i, D.sub.ij }.sub.i, with j fixed, approximately as a sine wave V.sub.j (t)=A.sub.j sin [2 .pi.s f.sub.c t+.phi..sub.j ], and determining an amplitude A.sub.j and a phase angle .phi..sub.j associated with converter number j for the set of values {t.sub.i, D.sub.ij }.sub.i ;
comparing the phase differences .DELTA..phi..sub.j2,j1 =.phi..sub.j2 -.phi..sub.j1 for 1.ltoreq.j1<j2.ltoreq.N with a corresponding desired phase difference number .DELTA..PHI..sub.j2,j1 =2 .pi.R(j2-j1)/N and, if the absolute difference .vertline..DELTA..PHI..sub.j2,j1 -.DELTA..phi..sub.j2,j1 .vertline. is larger than a selected positive phase angle error number .DELTA..PHI., determining that at least one of the converters number j1 and j2 has a phase error;
determining the amplitude differences .DELTA.A.sub.j4,j3 =A.sub.j4 -A.sub.j3 for 1.ltoreq.j3<j4.ltoreq.J and, when the absolute difference of at least one of these amplitude differences is larger than a selected positive amplitude error number .DELTA.A, determining that at least one of the converters number j3 and number j4 has an amplitude error;
when a phase error occurs in at least one of the converters number j1 and j2, adjusting a time delay of at least one clock pulse sequence so that the absolute difference .vertline..DELTA..PHI..sub.j2,j1 -.DELTA..phi..sub.j2,j1 .vertline. is no greater than .DELTA..PHI.;
and
when an amplitude error occurs in at least one of the converters number j3 and j4, adjusting an output signal amplitude of at least one of the converters so that the amplitude difference magnitude .vertline..DELTA.A.sub.j4,j3 .vertline. is no greater than .DELTA.A.

6 more elements

Dependencies are inferred from the claim text.