CN-0171 Datasheet, PDF (2/3 Pages) Analog Devices – Low Noise, Low Distortion Single-Ended Input Drive Circuit for Differential Input IF Sampling ADCs

CN-0171
The single-tone performance for an input frequency of 170 MHz
and a sampling rate of 122.88 MSPS is shown in Figure 3. Two-
tone performance is shown in Figure 4.
5
0
–5
–10
–15
–20
–25
–30
–35
–40
–45
0
50 100 150 200 250 300 350 400
FREQUENCY (MHz)
Figure 2. Normalized Frequency Response of the ADC Interface
Shown in Figure 1
0
SAMPLE FREQUENCY = 122.88MHz
SNRFS = 75.877dB
–20 INPUT FREQUENCY = 170MHZ
FUNDAMENTAL POWER = –1.044dBFS
SECOND HARMONIC POWER = –75.499dBc
–40 THIRD HARMONIC POWER = –80.003dBc
NOISE √Hz = –153.762dBFS/√Hz
–60
–80
–100
–120
–140
0
5 10 15 20 25 30 35 40 45 50 55 60 65
FREQUENCY (MHz)
Figure 3. Measured Single-Tone Performance of the Circuit Shown
in Figure 1 for an Input Frequency of 17 0MHz and Sampling Frequency
of 122.88 MSPS
Circuit Note
0
FUNDAMENTAL1 = –7.161dBFS
FUNDAMENTAL2 = –7.116dBFS
–20 _{IMD (2f1 – f2) = –66.07dBc}
IMD (2f2 – f1) = –67.588dBc
–40 ^{NOISE FLOOR = –150.84dBFS/√Hz}
–60
–80
–100
–120
–140
0
5 10 15 20 25 30 35 40 45 50 55 60 65
FREQUENCY (MHz)
Figure 4. Measured Two-Tone Performance of the Circuit Shown
in Figure 1 for Input Tones Centered at 170 MHz and a Sampling Rate
of 122.88 MSPS
COMMON VARIATIONS
The application circuit described here can be modified for any
IF frequency within the operating range of the ADL5535/ADL5536
and the AD9268. As an alternative to the AD9268, the AD9640,
the AD6657, or the AD9644 can be used for the ADC in this
application.
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