Datasheet

ADCS7476, ADCS7477, ADCS7478
www.ti.com SNAS192F –APRIL 2003–REVISED MARCH 2013
Timing Test Circuit ADCS7476/ADCS7477/ADCS7478 Timing Specifications (continued)
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, Boldface limits apply for T
A
= −40°C to +85°C:
all other limits T
A
= 25°C, unless otherwise noted.
(1)
Symbol Parameter Conditions Typical Limits Units
25 ns (max)
V
DD
= +2.7 to +3.6
6 ns (min)
SCLK Falling Edge to SDATA High
t
8
Impedance
(5)
25 ns (max)
V
DD
= +4.75 to +5.25
5 ns (min)
t
POWER-
Power-Up Time from Full Power-Down 1 µs
UP
(5) t
8
is derived from the time taken by the outputs to change by 0.5V with the loading circuit shown above. The measured number is then
adjusted to remove the effects of charging or discharging the 25pF capacitor. This means t
8
is the true bus relinquish time, independent
of the bus loading.
Specification Definitions
APERTURE DELAY is the variation in aperture delay from sample to sample. Aperture jitter manifests itself as
noise in the output.
APERTURE JITTER (APERTURE UNCERTAINTY) is the variation in aperture delay from sample to sample.
Aperture jitter manifests itself as noise in the output.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1
LSB.
DUTY CYCLE is the ratio of the time that a repetitive digital waveform is high to the total time of one period. The
specification here refers to the SCLK.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise
and Distortion or SINAD. ENOB is defined as (SINAD - 1.76) / 6.02 and says that the converter is
equivalent to a perfect ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH is a measure of the frequency at which the reconstructed output fundamental
drops 3 dB below its low frequency value for a full scale input.
GAIN ERROR is the deviation of the last code transition (111...110) to (111...111) from the ideal (V
REF
- 1.5 LSB
for ADCS7476 and ADCS7477, V
REF
- 1 LSB for ADCS7478), after adjusting for offset error.
INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from
negative full scale (½ LSB below the first code transition) through positive full scale (½ LSB above the last
code transition). The deviation of any given code from this straight line is measured from the center of that
code value.
INTERMODULATION DISTORTION (IMD) is the creation of additional spectral components as a result of two
sinusoidal frequencies being applied to the ADC input at the same time. It is defined as the ratio of the
power in the either the two second order or all four third order intermodulation products to the sum of the
power in both of the original frequencies. IMD is usually expressed in dBFS.
MISSING CODES are those output codes that will never appear at the ADC outputs. The ADCS7476/77/78 is
ensured not to have any missing codes.
OFFSET ERROR is the deviation of the first code transition (000...000) to (000...001) from the ideal (i.e. GND +
0.5 LSB for the ADCS7476 and ADCS7477, and GND + 1 LSB for the ADCS7478).
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal to the rms
value of the sum of all other spectral components below one-half the sampling frequency, not including
harmonics or DC.
SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD) Is the ratio, expressed in dB, of the rms value of
the input signal to the rms value of all of the other spectral components below half the clock frequency,
including harmonics but excluding DC.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the
input signal and the peak spurious signal, where a spurious signal is any signal present in the output
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