ADC32RF83 datasheet(121/138 Pages) TI

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Input Frequency (MHz)

100

1000

5000

D048

35 fs

50 fs

100 fs

150 fs

200 fs

Jitter

Jitter Ext _ Clock _ Input

Aperture_ ADC

Jitter

SNR

dBc

20log 2

S u

Quantization Noise

Thermal Noise

Jitter

SNR

SNRADC dBc

20log

121

ADC32RF80, ADC32RF83

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SBAS774A – MAY 2016 – REVISED DECEMBER 2016

Product Folder Links: ADC32RF80 ADC32RF83

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9.1.3 SNR and Clock Jitter

The signal-to-noise ratio (SNR) of the ADC is limited by three different factors: quantization noise, thermal noise,

and jitter, as shown in Equation 5. The quantization noise is typically not noticeable in pipeline converters and is

84 dB for a 14-bit ADC. The thermal noise limits the SNR at low input frequencies and the clock jitter sets the

SNR for higher input frequencies.

(5)

The SNR limitation resulting from sample clock jitter can be calculated by Equation 6:

(6)

The total clock jitter (TJitter) has two components: the internal aperture jitter (90 fS) is set by the noise of the clock

input buffer and the external clock jitter. TJitter can be calculated by Equation 7:

(7)

External clock jitter can be minimized by using high-quality clock sources and jitter cleaners as well as band-pass

filters at the clock input. A faster clock slew rate also improves the ADC aperture jitter.

The ADC32RF8x has a thermal noise of approximately 63 dBFS and an internal aperture jitter of 90 fS. The SNR,

depending on the amount of external jitter for different input frequencies, is shown in Figure 254.

Figure 254. ADC SNR vs Input Frequency and External Clock Jitter

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