AD9213 datasheet(32/110 Pages) AD

32 / 110 page

AD9213

Data Sheet

Rev. A | Page 32 of 110

CLOCK INPUT CONSIDERATIONS

The AD9213 has a low jitter clock receiver. For optimum

performance, drive the AD9213 sample clock inputs (CLK_x)

with a differential signal. This signal is typically ac-coupled to

the CLK_x pins via a transformer or clock drivers. These pins

are biased internally and require no additional external biasing.

Clock Jitter

High speed, high resolution ADCs are sensitive to the quality

of the clock signal.

The degradation in SNR at a given input frequency (fA) due only

to aperture jitter (tJ) can be calculated with the following equation:

SNR = 20 × log 10 (2 × π × fA × tJ)

In this equation, the rms aperture jitter represents the root sum

square of all jitter sources, including the clock input, analog

input signal, and ADC aperture jitter specifications.

Higher frequencies are increasingly sensitive to jitter (see

Figure 90).

130

120

110

100

1000

10000

ANALOG INPUT FREQUENCY (MHz)

12.5

100

200

400

800

Figure 90. Ideal SNR vs. Analog Input Frequency and Jitter

Treat the clock input as an analog signal in cases where aperture

jitter can affect the dynamic range of the AD9213. Separate

power supplies for clock drivers from the ADC output driver

supplies to avoid modulating the clock signal with digital noise.

If the clock is generated from another type of source (by gating,

dividing, or other methods), retime the clock by the original

clock at the last step. Refer to the AN-501 Application Note and

the AN-756 Application Note for more information about jitter

performance as it relates to ADCs.

Power-Down/Standby Mode

The AD9213 has a PDWN pin that can be used to configure the

device in power-down or standby mode.

Temperature Diode and Sensor

A thermal monitoring unit (TMU) is designed into the

AD9213. The die temperature can be read by SPI as described

in the TMU section.

The AD9213 also contains a diode-based temperature sensor

for measuring the temperature of the die. This diode can be

used in conjunction with external support components to serve

as a coarse temperature sensor to monitor the internal die

temperature.

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