AD6657
DIGITAL OUTPUTS
The AD6657 output drivers are configured to interface with
LVDS outputs using a DRVDD supply voltage of 1.8 V. The
output bits are DDR LVDS as shown in Figure 2. Applications
that require the ADC to drive large capacitive loads or large
fanouts may require external buffers or latches.
As described in Application Note AN-877, Interfacing to High
Speed ADCs via SPI, the data format can be selected for offset
binary or twos complement when using the SPI control.
TIMING
The AD6657 provides latched data with a pipeline delay of
nine clock cycles. Data outputs are available one propagation
delay (tPD) after the rising edge of the clock signal.
The length of the output data lines and the loads placed on
them should be minimized to reduce transients within the
AD6657. These transients can degrade converter dynamic
performance.
The lowest typical conversion rate of the AD6657 is 40 MSPS.
At clock rates below 40 MSPS, dynamic performance can degrade.
Data Clock Output (DCO)
The AD6657 provides a data clock output (DCO) signal intended
for capturing the data in an external register. The output data
for Channel A and Channel C is valid on the rising edge of
DCO; the output data for Channel B and Channel D is valid
on the falling edge of DCO. See Figure 2 for a graphical timing
description.
Table 11. Output Data Format
Input (V)
Condition (V)
VIN+ − VIN−
< −VREF − 0.5 LSB
VIN+ − VIN−
= −VREF
VIN+ − VIN−
=0
VIN+ − VIN−
= +VREF − 1.0 LSB
VIN+ − VIN−
> +VREF − 0.5 LSB
Offset Binary Output Mode
0000 0000 0000 0000
0000 0000 0000 0000
1000 0000 0000 0000
1111 1111 1111 1111
1111 1111 1111 1111
Twos Complement Mode
1000 0000 0000 0000
1000 0000 0000 0000
0000 0000 0000 0000
0111 1111 1111 1111
0111 1111 1111 1111
Rev. 0 | Page 21 of 32