SNAS717A April 2017 – October 2021 ADC12D1620QML-SP
PRODUCTION DATA
Refer to the PDF data sheet for device specific package drawings
The ADC12D1620 can be configured as either a 2-channel, 1.6 GSPS device (Non-DES mode) or a 1-channel 3.2-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+ must be driven with the exact same signal. VinI- and VinQ- must be driven with the exact same signal, which is the differential complement to the one driving VinI+ and VinQ+.
The input impedance for each I and Q input is 100-Ω differential (or 50-Ω single-ended), so the trace to each VinI+, VinI-, VinQ+, and VinQ- must always be 50-Ω single-ended. If a single I or Q input is being driven, then that input presents a 100-Ω differential load. For example, if a 50-Ω single-ended source is driving the ADC, a 1:2 balun transforms the impedance to 100-Ω differential. However, if the ADC is being driven in DESIQ mode, then the 100-Ω differential impedance from the I input appears in parallel with the Q input for a composite load of 50-Ω differential, and a 1:1 balun would be appropriate. See Figure 8-1 for an example circuit driving the ADC in DESIQ mode. A recommended part selection uses the mini-circuits TC1-1-13MA+ balun with Ccouple = 0.22 µF.
when only one channel is used in non-DES mode or the ADC is driven in DESI or DESQ mode, terminate the unused analog input to reduce any noise coupling into the ADC. See Table 8-1 for details.
MODE | POWER DOWN | COUPLING | RECOMMENDED TERMINATION |
---|---|---|---|
Non-DES | Yes | AC-DC | Tie Unused+ and Unused– to VBG |
DES/Non-DES | No | DC | Tie Unused+ and Unused– to VBG |
DES/Non-DES | No | AC | Tie Unused+ to Unused– |