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ADS6445, ADS6444
ADS6443, ADS6442
SLAS531 – MAY 2007
THD
+
10Log10
PS
PD
(6)
THD is typically given in units of dBc (dB to carrier).
Spurious-Free Dynamic Range (SFDR) – The ratio of the power of the fundamental to the highest other
spectral component (either spur or harmonic). SFDR is typically given in units of dBc (dB to carrier).
Two-Tone Intermodulation Distortion – IMD3 is the ratio of the power of the fundamental (at frequencies f1
and f2) to the power of the worst spectral component at either frequency 2f1–f2 or 2f2–f1. IMD3 is either given in
units of dBc (dB to carrier) when the absolute power of the fundamental is used as the reference, or dBFS (dB
to full scale) when the power of the fundamental is extrapolated to the converter’s full-scale range.
DC Power Supply Rejection Ratio (DC PSRR) – The DC PSSR is the ratio of the change in offset error to a
change in analog supply voltage. The DC PSRR is typically given in units of mV/V.
AC Power Supply Rejection Ratio (AC PSRR) – AC PSRR is the measure of rejection of variations in the
supply voltage by the ADC. If ∆Vsup is the change in supply voltage and ∆Vout is the resultant change of the
ADC output code (referred to the input), then
PSRR
+
20Log10
DVout
DVsup
,
expressed
in
dBc
(7)
Voltage Overload Recovery – The number of clock cycles taken to recover to less than 1% error after an
overload on the analog inputs. This is tested by separately applying a sine wave signal with 6dB positive and
negative overload. The deviation of the first few samples after the overload (from their expected values) is noted.
Common Mode Rejection Ratio (CMRR) – CMRR is the measure of rejection of variation in the analog input
common-mode by the ADC. If ∆Vcm_in is the change in the common-mode voltage of the input pins and ∆Vout
is the resultant change of the ADC output code (referred to the input), then
CMRR
+
20Log10
DVout
DVcm_in
,
expressed
in
dBc
(8)
Cross-Talk (only for multi-channel ADC)– This is a measure of the internal coupling of a signal from adjacent
channel into the channel of interest. It is specified separately for coupling from the immediate neighbouring
channel (near-channel) and for coupling from channel across the package (far-channel). It is usually measured
by applying a full-scale signal in the adjacent channel. Cross-talk is the ratio of the power of the coupling signal
(as measured at the output of the channel of interest) to the power of the signal applied at the adjacent channel
input. It is typically expressed in dBc.
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