AD7864

–16–

REV. A

AC Linearity Plots

The plots shown in Figure 18 below show typical DNL and INL

plots for the AD7864.

0

500

1000

1500

2000

2500

3000

3500

4000

3.00E–01

2.00E–01

1.00E–01

0.00E+00

–1.00E–01

–2.00E–01

–3.00E–01

ADC CODE

–5.00E–02

0.00E+00

5.00E–02

1.00E–01

1.50E–01

2.00E–01

2.50E–01

0

500

1000

1500

2000

2500

3000

3500

4000

ADC CODE

–2.50E–01

–2.00E–01

–1.50E–01

–1.00E–01

Figure 18. Typical DNL and INL Plots

Measuring Aperture Jitter

A convenient way to measure aperture jitter is to use the rela-

tionship it is known to have with SNR (Signal to Noise plus

distortion) given below:

SNR

f

where

ITTER

IN

J

=×

××

×









20

1

2

10

log

()

,

πσ

(3)

σ = rms time jitter

From Equation 3 above it can be seen that the signal-to-noise

ratio due to jitter degrades significantly with frequency. There-

fore, at low input frequencies the measured SNR performance

of the AD7864 is indicative of noise performance due to quanti-

zation noise and system noise only (72 dBs used as a typical

figure here).

Therefore, by measuring the overall SNR performance (includ-

ing noise due to jitter, system and quantization) of the AD7864 a

good estimation of the jitter performance of the AD7864 can be

calculated.

FREQUENCY – Hz

12

11

5

900000

1100000

950000

1000000

1050000

9

8

7

6

10

Figure 19. ENOBs of the AD7864 at 1 MHz

From Figure 19 above the ENOBs of the AD7864 at 1 MHz is

approximately 11 bits. This is equivalent to 68 dBs SNR.

From (3) above

70.2 dBs = 20

× log

σ = 49 ps where σ is the rms jitter of the AD7864