17.3.1 Input Control and Adjust
There are several features and configurations for the input of
the ADC12D1000/1600 so that it may be used in many dif-
ferent applications. This section covers AC/DC-coupled
Mode, input full-scale range adjust, input offset adjust, DES/
Non-DES Mode, and sampling clock phase adjust.
17.3.1.1 AC/DC-coupled Mode
The analog inputs may be AC or DC-coupled. See Sec-
tion 17.2.1.10 AC/DC-Coupled Mode Pin (VCMO) for informa-
tion on how to select the desired mode and Section 18.1.7
DC-coupled Input Signals and Section 18.1.6 AC-coupled In-
put Signals for applications information.
17.3.1.2 Input Full-Scale Range Adjust
The input full-scale range for the ADC12D1000/1600 may be
adjusted via Non-ECM or ECM. In Non-ECM, a control pin
selects a higher or lower value; see Section 17.2.1.9 Full-
Scale Input Range Pin (FSR). In ECM, the input full-scale
range may be adjusted with 15-bits of precision. See
VIN_FSR in Table 8 for electrical specification details. Note that
the higher and lower full-scale input range settings in Non-
ECM correspond to the mid and min full-scale input range
settings in ECM. It is necessary to execute an on-command
calibration following a change of the input full-scale range.
See Section 19.0 Register Definitions for information about
the registers.
17.3.1.3 Input Offset Adjust
The input offset adjust for the ADC12D1000/1600 may be
adjusted with 12-bits of precision plus sign via ECM. See
Section 19.0 Register Definitions for information about the
registers.
17.3.1.4 DES/Non-DES Mode
The ADC12D1000/1600 can operate in Dual-Edge Sampling
(DES) or Non-DES Mode. The DES Mode allows for a single
analog input to be sampled by both I- and Q-channels. One
channel samples the input on the rising edge of the sampling
clock and the other samples the same input signal on the
falling edge of the sampling clock. A single input is thus sam-
pled twice per clock cycle, resulting in an overall sample rate
of twice the sampling clock frequency, e.g. 2.0/3.2 GSPS with
a 1.0/1.6 GHz sampling clock. Since DES Mode uses both I-
and Q-channels to process the input signal, both channels
must be powered up for the DES Mode to function properly.
In Non-ECM, only the I-input may be used for the DES Mode
input. See Section 17.2.1.1 Dual Edge Sampling Pin (DES)
for information on how to select the DES Mode. In ECM, either
the I- or Q-input may be selected by first using the DES bit
(Addr: 0h, Bit 7) to select the DES Mode. The DEQ Bit (Addr:
0h, Bit: 6) is used to select the Q-input, but the I-input is used
by default. Also, both I- and Q-inputs may be driven externally,
i.e. DESIQ Mode, by using the DIQ bit (Addr: 0h, Bit 5). See
Section 18.1.2 Driving the ADC in DES Mode for more infor-
mation about how to drive the ADC in DES Mode.
The DESIQ Mode results in the best DES Mode bandwidth.
In general, the bandwidth decreases from Non-DES Mode to
DES Mode (specifically, DESI or DESQ) because both chan-
nels are sampling off the same input signal and non-ideal
effects introduced by interleaving the two channels lower the
bandwidth. Driving both I- and Q-channels externally (DESIQ
Mode) results in better bandwidth for the DES Mode because
each channel is being driven, which reduces routing losses.
In the DES Mode, the outputs must be carefully interleaved
in order to reconstruct the sampled signal. If the device is
programmed into the 1:4 Demux DES Mode, the data is ef-
fectively demultiplexed by 1:4. If the sampling clock is 1.0/1.6
GHz, the effective sampling rate is doubled to 2.0/3.2 GSPS
and each of the 4 output buses has an output rate of 500/800
MSPS. All data is available in parallel. To properly reconstruct
the sampled waveform, the four bytes of parallel data that are
output with each DCLK must be correctly interleaved. The
sampling order is as follows, from the earliest to the latest:
DQd, DId, DQ, DI. See Figure 6. If the device is programmed
into the Non-Demux DES Mode, two bytes of parallel data are
output with each edge of the DCLK in the following sampling
order, from the earliest to the latest: DQ, DI. See Figure 7.
17.3.1.5 DES Timing Adjust
The performance of the ADC12D1000/1600 in DES Mode
depends on how well the two channels are interleaved, i.e.
that the clock samples either channel with precisely a 50%
duty-cycle, each channel has the same offset (nominally code
2047/2048), and each channel has the same full-scale range.
The ADC12D1000/1600 includes an automatic clock phase
background adjustment in DES Mode to automatically and
continuously adjust the clock phase of the I- and Q-channels.
In addition to this, the residual fixed timing skew offset may
be further manually adjusted, and further reduce timing spurs
for specific applications. See the DES Timing Adjust (Addr:
7h). As the DES Timing Adjust is programmed from 0d to
127d, the magnitude of the Fs/2-Fin timing interleaving spur
will decrease to a local minimum and then increase again. The
default, nominal setting of 64d may or may not coincide with
this local minimum. The user may manually skew the global
timing to achieve the lowest possible timing interleaving spur.
17.3.1.6 Sampling Clock Phase Adjust
The sampling clock (CLK) phase may be delayed internally to
the ADC up to 825 ps in ECM. This feature is intended to help
the system designer remove small imbalances in clock distri-
bution traces at the board level when multiple ADCs are used,
or to simplify complex system functions such as beam steer-
ing for phase array antennas.
Additional delay in the clock path also creates additional jitter
when using the sampling clock phase adjust. Because the
sampling clock phase adjust delays all clocks, including the
DCLKs and output data, the user is strongly advised to use
the minimal amount of adjustment and verify the net benefit
of this feature in his system before relying on it.
17.3.2 Output Control and Adjust
There are several features and configurations for the output
of the ADC12D1000/1600 so that it may be used in many dif-
ferent applications. This section covers DDR clock phase,
LVDS output differential and common-mode voltage, output
formatting, Demux/Non-demux Mode, Test Pattern Mode,
and Time Stamp.
17.3.2.1 DDR Clock Phase
The ADC12D1000/1600 output data is always delivered in
Double Data Rate (DDR). With DDR, the DCLK frequency is
half the data rate and data is sent to the outputs on both edges
of DCLK; see Figure 13. The DCLK-to-Data phase relation-
ship may be either 0° or 90°. For 0° Mode, the Data transitions
on each edge of the DCLK. Any offset from this timing is
tOSK; see Table 14 for details. For 90° Mode, the DCLK tran-
sitions in the middle of each Data cell. Setup and hold times
for this transition, tSU and tH, may also be found in Table 14.
The DCLK-to-Data phase relationship may be selected via
the DDRPh Pin in Non-ECM (see Section 17.2.1.3 Dual Data
Rate Phase Pin (DDRPh)) or the DPS bit in the Configuration
Register (Addr: 0h; Bit: 14) in ECM.
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ADC12D1000/ADC12D1600