CS5014 datasheet(30/40 Pages) CIRRUS

30 / 40 page

Clock Feedthrough in the CS5014 and CS5016

Maintaining the integrity of analog signals in the

presence of digital switching noise is a difficult

problem. The CS5014/16 can be synchronized to

the digital system using the CLKIN input to

avoid conversion errors due to asynchronous in-

terference. However, digital interference will still

affect sampling purity due to coupling between

the CS5014/16’s analog input and master clock.

The effect of clock feedthrough depends on the

sampling conditions. If the sampling signal at the

HOLD input is synchronized to the master clock,

clock feedthrough will appear as a dc offset at the

CS5014/16’s output. The offset could theoreti-

cally reach the peak coupling magnitude

(Figure 34), but the probability of this occurring

is small since the peaks are spikes of short dura-

tion.

If sampling is performed asynchronously with the

master clock, clock feedthrough will appear as an

ac error at the CS5014/16’s output. With a fixed

Analog Input

Source Impedance

200

4MHz

2MHz

Master Clock

Clock Feedthrough

Int/Ext

Freq

Internal

External

2MHz

4MHz

RMS

Peak-to-Peak

15uV

25uV

40uV

25uV

80uV

70uV

110uV

150uV

110uV

325uV

Figure 35. Examples of Measured Clock Feedthrough

Signal

Amplitude

Relative to

Full Scale

Input Frequency

0dB

-20dB

-40dB

-60dB

-80dB

-100dB

-120dB

28 kHz

Sampling Rate: 56 kHz

Full Scale: 9V p-p

S/(N+D): 81.5 dB

12 kHz

Figure 3

0. CS5014 FFT plot with 12 kHz

Full

-scale Input

Signal

Amplitude

Relative to

Full Scale

Input Frequency

0dB

-20dB

-40dB

-60dB

-80dB

-100dB

-120dB

25 kHz

Sampling Rate: 50 kHz

Full Scale: 9V p-p

S/(N+D): 84.3 dB

12 kHz

Figure 3

2. CS5016 FFT plot with 12 kHz

Full

-scale Input

Signal

Amplitude

Relative to

Full Scale

Input Frequency

0dB

-20dB

-40dB

-60dB

-80dB

-100dB

-120dB

25 kHz

Sampling Rate: 50 kHz

Full Scale: 9V p-p

S/(N+D): 71.9 dB

12 kHz

Figure 3

3. CS5016 FFT plot with 12 kHz

-20 dB Input

Signal

Amplitude

Relative to

Full Scale

Input Frequency

0dB

-20dB

-40dB

-60dB

-80dB

-100dB

-120dB

28 kHz

Sampling Rate: 56 kHz

Full Scale: 9V p-p

S/(N+D): 64.6 dB

12 kHz

Figure 3

1. CS5014 FFT plot with 12 kHz

-20 dB Input

CS5012A, CS5014, CS5016

2-36

DS14F8

CS5012A CS5014 CS5016

DS14F9

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