Specifications

ADC12D1600/1000RF
V
IN
I+
50:
Source
V
IN
I-
1:1 Balun
C
couple
C
couple
100:
V
IN
Q+
V
IN
Q-
100:
C
couple
C
couple
ADC12D1000RF, ADC12D1600RF
SNAS519G –JULY 2011–REVISED APRIL 2013 www.ti.com
samples data on the falling edge of CLK+. The digital equivalent of that data is available at the digital
outputs a constant number of sampling clock cycles later for the DI, DQ, DId and DQd output buses, a.k.a.
Latency, depending on the demultiplex mode which is selected. In addition to the Latency, there is a
constant output delay, t
OD
, before the data is available at the outputs. See t
OD
in the Timing Diagrams.
See t
LAT
, t
AD
, and t
OD
in Converter Electrical Characteristics AC Electrical Characteristics.
6.4.1.2 Driving the ADC in DES Mode
The ADC12D1600/1000RF can be configured as either a 2-channel, 1600/1000 GSPS device (Non-DES
Mode) or a 1-channel 3.2/2.0 GSPS device (DES Mode). When the device is configured in DES Mode,
there is a choice for with which input to drive the single-channel ADC. These are the 3 options:
DES – externally driving the I-channel input only. This is the default selection when the ADC is configured
in DES Mode. It may also be referred to as “DESI” for added clarity.
DESQ – externally driving the Q-channel input only.
DESIQ, DESCLKIQ – externally driving both the I- and Q-channel inputs. VinI+ and VinQ+ should be
driven with the exact same signal. VinI- and VinQ- should be driven with the exact same signal, which is
the differential compliment to the one driving VinI+ and VinQ+.
The input impedance for each I- and Q-input is 100Ω differential (or 50Ω single-ended), so the trace to
each VinI+, VinI-, VinQ+, and VinQ- should always be 50Ω single-ended. If a single I- or Q-input is being
driven, then that input will present a 100Ω differential load. For example, if a 50Ω single-ended source is
driving the ADC, then a 1:2 balun will transform the impedance to 100Ω differential. However, if the ADC
is being driven in DESIQ Mode, then the 100Ω differential impedance from the I-input will appear in
parallel with the Q-input for a composite load of 50Ω differential and a 1:1 balun would be appropriate.
See Figure 6-5 for an example circuit driving the ADC in DESIQ Mode. A recommended part selection is
using the Mini-Circuits TC1-1-13MA+ balun with Ccouple = 0.22µF.
Figure 6-5. Driving DESIQ Mode
In the case that only one channel is used in Non-DES Mode or that the ADC is driven in DESI or DESQ
Mode, the unused analog input should be terminated to reduce any noise coupling into the ADC. See
Table 6-9 for details.* The timing for these figures is shown for the one input only (I or Q). However, both
I- and Q-inputs may be used. For this case, the I-channel functions precisely the same as the Q-channel,
with VinI, DCLKI, DId and DI instead of VinQ, DCLKQ, DQd and DQ. Both I- and Q-channel use the same
CLK.
50 Functional Description Copyright © 2011–2013, Texas Instruments Incorporated
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