Circuit Note

CN-0385

Rev. 0 | Page 9 of 13

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.

Figure 15. Settling Time Evaluation Setup Using DC Calibrators

Figure 16. Settling Time Evaluation Setup Using AC Signal Generator

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.

Figure 17. Mean Code Error vs. Voltage Step Size, Gain = 0.4

Figure 18. Mean Code Error vs. Voltage Step Size, Gain = 0.8

–120

–100

–80

–60

–40

–20

0

1

10

100

INPUT FREQUENCY (kHz)

GAIN = 0.4dB

GAIN = 0.8dB

GAIN = 1.6dB

GAIN = 3.2dB

EVAL-CN0385-FMCZ

C1–

C1+

C2+

C2–

GND

+

–

DVC

DVC

+

–

EVAL-SDP-CH1Z

EVAL-CN0385-FMCZ

C5–

C5+

C7–

C7+

GND

EVAL-SDP-CH1Z

+ G

AP SYS-2712

+

–

–

G

ADA4627

BUFFERS

–250

–200

–150

–100

–50

0

50

100

150

200

250

300

0

5

10

15

20

STEP SIZE (V)

100kSPS, CHANNEL A

100kSPS, CHANNEL B

500kSPS, CHANNEL A

500kSPS, CHANNEL B

800kSPS, CHANNEL A

800kSPS, CHANNEL B

–250

–200

–150

–100

–50

0

50

100

150

200

250

300

350

0

5

10

15

20

STEP SIZE (V)

100kSPS, CHANNEL A

100kSPS, CHANNEL B

500kSPS, CHANNEL A

500kSPS, CHANNEL B

800kSPS, CHANNEL A

800kSPS, CHANNEL B