ADC31RF80 datasheet(32/142 Pages) TI2

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CLKINP

100

SYSREFP

SYSREF

Capture

Delay

CLKINM

SYSREFM

Clock Amplitude (vPP)

0.2

100

150

200

250

300

350

D061

fIN = 1 GHz

fIN = 2 GHz

ADC31RF80

SBAS860 – AUGUST 2017

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Feature Description (continued)

The analog-to-digital converter (ADC) aperture jitter is a function of the clock amplitude applied to the pins.

Figure 88 shows the equivalent aperture jitter for input frequencies at a 1-GHz and a 2-GHz input. Depending on

the clock frequency, a matching circuit can be designed in order to maximize the clock amplitude.

Figure 88. Equivalent Aperture Jitter vs Input Clock Amplitude

8.3.3 SYSREF Input

The SYSREF signal is a periodic signal that is sampled by the ADC31RF80 device clock and is used to align the

boundary of the local multiframe clock inside the data converter. SYSREF is also used to reset critical blocks

[such as the clock divider for the interleaved ADCs, numerically-controlled oscillators (NCOs), decimation filters

and so forth].

The SYSREF input requires external biasing. Furthermore, SYSREF must be established before the SPI

registers are programmed. A programmable delay on the SYSREF input, as shown in Figure 89, is available to

help with skew adjustment when the sampling clock and SYSREF are not provided from the same source.

Figure 89. SYSREF Internal Circuit Diagram

ADC31RF80 Datasheet(PDF) 32 Page - Texas Instruments