AD6655 Analog Devices, AD6655 Datasheet - Page 34

• Manufacturer Part Number: AD6655
• Description: IF Diversity Receiver
• Manufacturer: Analog Devices

AD6655
The clock input should be treated as an analog signal in cases
where aperture jitter may affect the dynamic range of the AD6655.
Power supplies for clock drivers should be separated from the
ADC output driver supplies to avoid modulating the clock signal
with digital noise. Low jitter, crystal-controlled oscillators make
the best clock sources. If the clock is generated from another type
of source (by gating, dividing, or another method), it should be
retimed by the original clock at the last step.
Refer to Application Note AN501 and Application Note AN756 for
more information about jitter performance as it relates to ADCs
(see www.analog.com).
POWER DISSIPATION AND STANDBY MODE
As shown in Figure 64 through Figure 67, the power dissipated
by the AD6655 is proportional to its sample rate. In CMOS
output mode, the digital power dissipation is determined
primarily by the strength of the digital drivers and the load on
each output bit. The maximum DRVDD current (I
calculated by
where N is the number of output bits (30, in the case of the
AD6655, assuming the FD bits are inactive).
This maximum current occurs when every output bit switches
on every clock cycle, that is, a full-scale square wave at the
Nyquist frequency of f
is established by the average number of output bits switching,
which is determined by the sample rate and the characteristics
of the analog input signal. Reducing the capacitive load presented
to the output drivers can minimize digital power consumption.
The data in Figure 64 through Figure 67 was taken using the same
operating conditions as those used for the Typical Performance
Characteristics, with a 5 pF load on each output driver.
I
DRVDD
75
70
65
60
55
50
45
1
MEASURED
= V
Figure 63. SNR vs. Input Frequency and Jitter
DRVDD
× C
CLK
LOAD
INPUT FREQUENCY (MHz)
10
/2. In practice, the DRVDD current
× f
CLK
× N
100
0.05ps
0.20ps
0.50ps
1.00ps
1.50ps
2.00ps
2.50ps
3.00ps
DRVDD
1000
) can be
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1.50
1.25
1.00
0.75
0.50
0.25
1.50
1.25
1.00
0.75
0.50
0.25
1.25
1.00
0.75
0.50
0.25
0
0
0
0
0
0
Figure 64. AD6655-150 Power and Current vs. Sample Rate
Figure 65. AD6655-125 Power and Current vs. Sample Rate
Figure 66. AD6655-105 Power and Current vs. Sample Rate
I
AVDD
I
AVDD
25
25
25
I
AVDD
50
SAMPLE RATE (MSPS)
SAMPLE RATE (MSPS)
SAMPLE RATE (MSPS)
50
I
I
DRVDD
50
DVDD
75
TOTAL POWER
TOTAL POWER
I
DRVDD
I
I
I
DRVDD
DVDD
DVDD
75
TOTAL POWER
100
75
100
125
100
150
125
0.6
0.5
0.4
0.3
0.2
0.1
0
0.6
0.5
0.4
0.3
0.2
0.1
0
0.5
0.4
0.3
0.2
0.1
0