The circuit of Figure 11 converts a single-ended input
signal to fully differential just as Figure 10. However,
Figure 11 utilizes an additional transformer to improve
the common-mode rejection, allowing high-frequency
signals beyond the Nyquist frequency. The two sets of
termination resistors provide an equivalent 75Ω termi-
nation to the signal source. The second set of termina-
tion resistors connects to COM, providing the correct
input common-mode voltage. Two 0Ω resistors in series
with the analog inputs allow high IF input frequencies.
These 0Ω resistors can be replaced with low-value
resistors to limit the input bandwidth.
Single-Ended AC-Coupled Input Signal
Figure 12 shows an AC-coupled, single-ended input
application. The MAX4108 provides high speed, high
bandwidth, low noise, and low distortion to maintain the
input signal integrity.
MAX1209
12-Bit, 80Msps, 3.3V IF-Sampling ADC
______________________________________________________________________________________ 21
N.C.
N.C. N.C.
N.C.
RESISTORS TO LIMIT THE BANDWIDTH.
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