Specifications

ADC12D1600/1000RF
V
IN
+
50:
Source
V
IN
-
1:2 Balun
C
couple
C
couple
100:
V
IN
+
V
IN
-
V
CMO
ADC12D1600/1000RF
C
couple
C
couple
ADC12D1000RF, ADC12D1600RF
SNAS519G –JULY 2011–REVISED APRIL 2013 www.ti.com
When the AC-coupled Mode is selected, an analog input channel that is not used (e.g. in DES Mode)
should be connected to AC ground, e.g. through capacitors to ground . Do not connect an unused analog
input directly to ground.
Figure 6-6. AC-coupled Differential Input
The analog inputs for the ADC12D1600/1000RF are internally buffered, which simplifies the task of driving
these inputs and the RC pole which is generally used at sampling ADC inputs is not required. If the user
desires to place an amplifier circuit before the ADC, care should be taken to choose an amplifier with
adequate noise and distortion performance, and adequate gain at the frequencies used for the application.
6.4.1.7 DC-coupled Input Signals
In DC-coupled Mode, the ADC12D1600/1000RF differential inputs must have the correct common-mode
voltage. This voltage is provided by the device itself at the V
CMO
output pin. It is recommended to use this
voltage because the V
CMO
output potential will change with temperature and the common-mode voltage of
the driving device should track this change. Full-scale distortion performance falls off as the input common
mode voltage deviates from V
CMO
. Therefore, it is recommended to keep the input common-mode voltage
within 100 mV of V
CMO
(typical), although this range may be extended to ±150 mV (maximum). See V
CMI
in Converter Electrical Characteristics Analog Input/Output and Reference Characteristics and ENOB vs.
V
CMI
in Typical Performance Plots . Performance in AC- and DC-coupled Mode are similar, provided that
the input common mode voltage at both analog inputs remains within 100 mV of V
CMO
.
6.4.1.8 Single-Ended Input Signals
The analog inputs of the ADC12D1600/1000RF are not designed to accept single-ended signals. The best
way to handle single-ended signals is to first convert them to differential signals before presenting them to
the ADC. The easiest way to accomplish single-ended to differential signal conversion is with an
appropriate balun-transformer, as shown in Figure 6-7.
Figure 6-7. Single-Ended to Differential Conversion Using a Balun
When selecting a balun, it is important to understand the input architecture of the ADC. The impedance of
the analog source should be matched to the ADC12D1600/1000RF's on-chip 100Ω differential input
termination resistor. The range of this termination resistor is specified as R
IN
in Converter Electrical
Characteristics Analog Input/Output and Reference Characteristics.
52 Functional Description Copyright © 2011–2013, Texas Instruments Incorporated
Submit Documentation Feedback
Product Folder Links: ADC12D1000RF ADC12D1600RF