AD9684 datasheet(29/65 Pages) AD

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AD9684

Data Sheet

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10 BITS

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8 BITS

RMS CLOCK JITTER REQUIREMENT

ANALOG INPUT FREQUENCY (MHz)

Figure 53. Ideal SNR vs. Analog Input Frequency and Jitter

Treat the clock input as an analog signal when aperture jitter

may affect the dynamic range of the AD9684. Separate the power

supplies for the 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. For more in-depth information about jitter

performance as it relates to ADCs, see the AN-501 Application

Note and the AN-756 Application Note.

Figure 54 shows the estimated SNR of the AD9684 across the

input frequency for different clock induced jitter values. Estimate

the SNR using the following equation:























 −











 −

10log

(dBFS)

JITTER

ADC

SNR

10M

100M

10G

INPUT FREQUENCY (Hz)

25fs

50fs

75fs

100fs

125fs

150fs

175fs

200fs

Figure 54. Estimated SNR Degradation for the AD9684 vs. Input Frequency

and Clock Jitter

POWER-DOWN/STANDBY MODE

The AD9684 has a PDWN/STBY pin that configures the device

in power-down or standby mode. The default operation is the

power-down function. The PDWN/STBY pin is a logic high pin.

The power-down option can also be set via Register 0x03F and

TEMPERATURE DIODE

The AD9684 contains a diode-based temperature sensor for

measuring the temperature of the die. This diode can output a

voltage and serve as a coarse temperature sensor to monitor the

internal die temperature.

The temperature diode voltage can be output to the FD_A pin

using the SPI. Use Register 0x028, Bit 0 to enable or disable the

diode. Register 0x028 is a local register. Channel A must be

selected in the device index register (Register 0x008) to enable

the temperature diode readout. Configure the FD_A pin to

output the diode voltage by programming Register 0x040,

Bits[2:0]. See Table 29 for more information.

The voltage response of the temperature diode (with SPIVDD =

1.8 V) is shown in Figure 55.

TEMPERATURE (°C)

0.60

0.65

0.70

0.75

0.80

0.85

0.90

–55 –45 –35 –25 –15 –5

15 25 35 45 55 65 75 85 95 105 115 125

Figure 55. Diode Voltage vs. Temperature

Rev. 0 | Page 28 of 64

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