CN0385 Datasheet, PDF (9/13 Pages) Analog Devices – Devices Connected

Circuit Note
0
GAIN = 0.4dB
GAIN = 0.8dB
GAIN = 1.6dB
–20 GAIN = 3.2dB
–40
–60
–80
–100
–120
1
10
100
INPUT FREQUENCY (kHz)
Figure 14. THD Measured for Various Input Frequencies on a Single,
Static Channel
System Performance with Channel Switching
Several tests were performed to evaluate the performance of the
system when scanning multiple channels. Experiments using
precision dc sources measured the error in output code with
respect to sample rate (see the Circuit Note CN-0269 for similar
tests) and voltage step size between channels. AC performance was
also measured for switching between two out of phase, full-scale
inputs from a precision ac source (Audio Precision AP SYS-2712).
Figure 15 and Figure 16 show the test setup for dc and ac
performance tests, respectively. The channel switching rate is
the rate at which the ADG5207 switches from one channel to
another, and is equivalent to the sample rate of the AD4003.
DVC
+–
DVC
+–
EVAL-CN0385-FMCZ
C1–
C1+
C2+
C2–
GND
EVAL-SDP-CH1Z
Figure 15. Settling Time Evaluation Setup Using DC Calibrators
AP SYS-2712
+G – +G –
EVAL-CN0385-FMCZ
ADA4627
BUFFERS
C5–
C5+
C7–
C7+
GND
EVAL-SDP-CH1Z
Figure 16. Settling Time Evaluation Setup Using AC Signal Generator
CN-0385
The dc tests involved varying the voltage step size between the
two channels and the channel switching rate. The channel
switching rate was varied from 50 kHz to 1 MHz in 50 kHz
increments. The voltage step size was varied over different
ranges for each of the gain configurations. A mean code result
was measured for each channel for each voltage step size and
channel switching rate by averaging 8,192 samples taken on
each channel. A mean code result was also measured for each
channel in the static case (no switching between channels). The
mean code errors discussed below were found by taking the
difference between the mean codes measured for the static case
and for the switching channels.
Figure 17, Figure 18, Figure 19, and Figure 20 show the mean
code error for various voltage step sizes at several switching rates
in each of the four gain configurations. Figure 21, Figure 22,
Figure 23, and Figure 24 show the mean code error for full-scale
voltage steps at various switching rates in each of the four gain
configurations.
300
100kSPS, CHANNEL A
250
100kSPS, CHANNEL B
500kSPS, CHANNEL A
200
500kSPS, CHANNEL B
800kSPS, CHANNEL A
150
800kSPS, CHANNEL B
100
50
0
–50
–100
–150
–200
–250
0
5
10
15
20
STEP SIZE (V)
Figure 17. Mean Code Error vs. Voltage Step Size, Gain = 0.4
350
100kSPS, CHANNEL A
300
100kSPS, CHANNEL B
500kSPS, CHANNEL A
250
500kSPS, CHANNEL B
800kSPS, CHANNEL A
200
800kSPS, CHANNEL B
150
100
50
0
–50
–100
–150
–200
–250
0
5
10
15
20
STEP SIZE (V)
Figure 18. Mean Code Error vs. Voltage Step Size, Gain = 0.8
Rev. 0 | Page 9 of 13