AD9684 Datasheet, PDF (28/64 Pages) Analog Devices – Dual, 14-Bit, 1.25 GSPS, 1.2 V/2.5 V, Analog-to-Digital Converter

AD9684
Product
Overview
Online
Documentation
130
RMS CLOCK JITTER REQUIREMENT
120
110
100
16 BITS
90
14 BITS
80
70
10 BITS
60
50 ^{8 BITS}
40
30
1
0.125ps
0.25ps
0.5ps
1.0ps
2.0ps
10
100
ANALOG INPUT FREQUENCY (MHz)
12 BITS
1000
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:
SNR (dBFS)
=
10log_{}10^{}
− SNR_ADC
10

+ 10^{}
− SNR_JITTER
10





75
70
65
25fs
50fs
60
75fs
100fs
125fs
55
150fs
175fs
200fs
50
45
1M
10M
100M
1G
10G
INPUT FREQUENCY (Hz)
Figure 54. Estimated SNR Degradation for the AD9684 vs. Input Frequency
and Clock Jitter
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Data Sheet
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
Register 0x040.
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.
0.90
0.85
0.80
0.75
0.70
0.65
0.60
–55 –45 –35 –25 –15 –5
5 15 25 35 45 55 65 75 85 95 105 115 125
TEMPERATURE (°C)
Figure 55. Diode Voltage vs. Temperature
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