AD7927 Analog Devices, AD7927 Datasheet - Page 9

• Manufacturer Part Number: AD7927
• Description: 8-Channel, 200 kSPS, 12-Bit ADC with Sequencer in 20-Lead TSSOP
• Manufacturer: Analog Devices

Specifications of AD7927

• Resolution (bits): 12bit
• # Chan: 8
• Sample Rate: 200kSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref),Uni (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: SOP

Data Sheet
Signal-to-(Noise + Distortion) Ratio (SINAD)
This is the measured ratio of signal-to-(noise + 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
is dependent on the number of quantization levels in the digiti-
zation process; the more levels, the smaller the quantization
noise. The theoretical signal-to-(noise + distortion) ratio for
an ideal N-bit converter with a sine wave input is given by
Thus, for a 12-bit converter, this is 74 dB. Figure 5 shows the
signal-to-(noise + distortion) ratio performance vs. input fre-
quency for various supply voltages while sampling at 200 kSPS
with an SCLK of 20 MHz.
Signal-to-(Noise + Distortion) = (6.02N + 1.76)dB
S
/2), excluding dc. The ratio
Rev. C | Page 9 of 28
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the
fundamental. For the AD7927, it is defined as:
where:
V
V
through the sixth harmonics.
Figure 7 shows a graph of total harmonic distortion vs. analog
input frequency for various supply voltages, and Figure 8 shows
a graph of total harmonic distortion vs. analog input frequency
for various source impedances (see the Analog Input section).
1
2
, V
is the rms amplitude of the fundamental.
THD
3
, V
4
, V
(
dB
5
, and V
)
=
20
log
6
are the rms amplitudes of the second
V
2
2
+
V
3
2
+
V
V
1
4
2
+
V
5
2
+
V
6
2
AD7927