AD7934-6 Analog Devices, AD7934-6 Datasheet - Page 12

• Manufacturer Part Number: AD7934-6
• Description: 4-Channel, 625 kSPS, 12-Bit Parallel ADC with a Sequencer
• Manufacturer: Analog Devices

Specifications of AD7934-6

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 625kSPS
• Interface: Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: Uni (Vref),Uni (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: SOP

AD7934-6
Track-and-Hold Acquisition Time
The track-and-hold amplifier returns to track mode at the end
of conversion. The track-and-hold acquisition time is the time
required for the output of the track-and-hold amplifier to reach
its final value, within ±½ LSB, after the end of conversion.
Signal-to-Noise and Distortion Ratio (SINAD)
This is the measured ratio of signal-to-noise and distortion at
the output of the ADC. The signal is the rms amplitude of the
fundamental. Noise is the sum of all nonfundamental signals up
to half the sampling frequency (f
ratio is dependent on the number of quantization levels in the
digitization process; the more levels, the smaller the
quantization noise.
The theoretical SINAD ratio for an ideal N-bit converter with a
sine wave input is given by:
Thus, for a 12-bit converter, SINAD is 74 dB.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the
fundamental. For the AD7934-6, it is defined as:
where:
V
V
through the sixth harmonics.
1
2
, V
is the rms amplitude of the fundamental.
SINAD = (6.02 N + 1.76) dB
THD
3
, V
4
, V
( )
dB
5
, and V
=
−
20
6
are the rms amplitudes of the second
log
⎛
⎜
⎜
⎝
V
2
2
+
SAMPLE
V
3
2
/2), excluding dc. The
+
V
V
1
4
2
+
V
5
2
+
V
6
2
⎞
⎟
⎟
⎠
Rev. B | Page 12 of 28
Peak Harmonic or Spurious Noise
This is defined as the ratio of the rms value of the next largest
component in the ADC output spectrum (up to f
excluding dc) to the rms value of the fundamental. Normally,
the value of this specification is determined by the largest
harmonic in the spectrum, but for ADCs where the harmonics
are buried in the noise floor, it is a noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities creates distortion
products at sum and difference frequencies of mfa ± nfb, where
m, n = 0, 1, 2, 3, and so on. Intermodulation distortion terms
are those for which neither m nor n are equal to zero. For
example, the second-order terms include (fa + fb) and (fa − fb),
while the third-order terms include (2fa + fb), (2fa − fb), (fa + 2fb),
and (fa − 2fb).
The AD7934-6 is tested using the CCIF standard where two
input frequencies near the top end of the input bandwidth are
used. In this case, the second-order terms are usually distanced
in frequency from the original sine waves, while the third-order
terms are usually at a frequency close to the input frequencies.
As a result, the second- and third-order terms are specified
separately. The intermodulation distortion is calculated per the
THD specification, as the ratio of the rms sum of the individual
distortion products to the rms amplitude of the sum of the
fundamentals, expressed in dB.
SAMPLE
/2 and