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Data Sheet

AD9680

Rev. C | Page 43 of 97

IF undersampling applications are particularly sensitive to jitter

(see Figure 138).

130

120

110

100

1000

10000

ANALOG INPUT FREQUENCY (MHz)

12.5

100

200

400

800

Figure 138. Ideal SNR vs. Input Frequency and Jitter

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

jitter may affect the dynamic range of the AD9680. 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 in-depth information about

jitter performance as it relates to ADCs.

Figure 139 shows the estimated SNR of the AD9680-1000 across

input frequency for different clock induced jitter values. The

SNR can be estimated by using the following equation:























 −











 −

10log

(dBFS)

JITTER

ADC

SNR

INPUT FREQUENCY (MHz)

100

10K

25fs

50fs

75fs

100fs

125fs

150fs

175fs

200fs

Figure 139. Estimated SNR Degradation for the AD9680-1000 vs.

Input Frequency and RMS Jitter

Power-Down/Standby Mode

The AD9680 has a PDWN/STBY pin that can be used to

configure the device in power-down or standby mode. The

default operation is PDWN. The PDWN/STBY pin is a logic

high pin. When in power-down mode, the JESD204B link is

disrupted. The power-down option can also be set via

In standby mode, the JESD204B link is not disrupted and

transmits zeros for all converter samples. This can be changed

using Register 0x571, Bit 7 to select /K/ characters.

Temperature Diode

The AD9680 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 (0x008) to enable the

temperature diode readout. Configure the FD_A pin to output

the diode voltage by programming Register 0x040[2:0]. See

Table 36 for more information.

The voltage response of the temperature diode (SPIVDD =

1.8 V) is shown in Figure 140.

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 140. Temperature Diode Voltage vs. Temperature

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