ADC31RF80 Datasheet, PDF (29/136 Pages) Texas Instruments – 3-GSPS Telecom Receiver and Feedback Device

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ADC31RF80
SBAS860 – AUGUST 2017
Feature Description (continued)
The input impedance of analog inputs can also be modelled as parallel combination of equivalent resistance and
capacitance. Figure 82 and Figure 83 show how equivalent impedance (C_IN and R_IN) vary over frequency.
3
0.07
2
0.06
1
0.05
0
0.04
-1
0.03
-2
0.02
-3
0
500
1000 1500 2000 2500 3000
Input Frequency (MHz)
D063
Figure 82. Differential Input Capacitance vs
Input Frequency
0.01
0
500 1000 1500 2000 2500 3000
Input Frequency (MHz)
D06041
Figure 83. Differential Input Resistance vs Input Frquency
Each input pin (INP, INM) must swing symmetrically between (CM + 0.3375 V) and (CM – 0.3375 V), resulting in
a 1.35-V_PP (default) differential input swing. Figure 84 shows that the input sampling circuit has a 3-dB bandwidth
that extends up to approximately 3.2 GHz.
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
100
100 Ohm Source
50 Ohm Source
200 300 500 700 1000 2000 3000 5000
Input Frequency (MHz)
D062
Figure 84. Input Bandwidth with a 100-Ω Source Resistance
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