EVAL-AD7933CB AD [Analog Devices], EVAL-AD7933CB Datasheet - Page 18

• Manufacturer Part Number: EVAL-AD7933CB
• Description: 4-Channel, 1.5 MSPS, 12-Bit and 10-Bit Parallel ADCs with a Sequencer
• Manufacturer: AD [Analog Devices]

AD7933/AD7934
CIRCUIT INFORMATION
The AD7933/AD7934 are fast, 4-channel, 12-bit and10-bit,
single-supply, successive approximation analog-to-digital
converters. The parts operate from either a 2.7 V to 3.6 V or
4.75 V to 5.25 V power supply and feature throughput rates up
to 1.5 MSPS.
The AD7933/AD7934 provide the user with an on-chip track-
and-hold, an internal accurate reference, an analog-to-digital
converter, and a parallel interface housed in a 28-lead TSSOP
package.
The AD7933/AD7934 have four analog input channels that can
be configured to be four single-ended inputs, two fully
differential pairs, or two pseudo-differential pairs. There is an
on-chip channel sequencer that allows the user to select a
consecutive sequence of channels through which the ADC can
cycle with each falling edge of CONVST .
The analog input range for the AD7933/AD7934 is 0 to V
0 to 2 × V
control register. The output coding of the ADC can be either
binary or twos complement, depending on the status of the
CODING bit in the control register.
The AD7933/AD7934 provide flexible power management
options to allow users to achieve the best power performance
for a given throughput rate. These options are selected by
programming the power management bits, PM1 and PM0, in
the control register.
CONVERTER OPERATION
The AD7933/AD7934 are a successive approximation ADC
based on two capacitive DACs. Figure 18 and Figure 19 show
simplified schematics of the ADC in acquisition and conversion
phase, respectively. The ADC comprises of control logic, a SAR,
and two capacitive DACs. Both figures show the operation of
the ADC in differential/pseudo-differential mode. Single-ended
mode operation is similar but V
In the acquisition phase, SW3 is closed, SW1 and SW2 are in
Position A, the comparator is held in a balanced condition, and
the sampling capacitor arrays acquire the differential signal on
the input.
V
V
IN+
IN–
REF
B
A
A
B
, depending on the status of the RANGE bit in the
V
REF
SW1
SW2
Figure 18. ADC Acquisition Phase
C
C
S
S
SW3
IN−
COMPARATOR
is internally tied to AGND.
CAPACITIVE
CAPACITIVE
CONTROL
LOGIC
DAC
DAC
REF
Rev. PrG | Page 18 of 32
or
When the ADC starts a conversion (Figure 19), SW3 will open
and SW1 and SW2 will move to Position B, causing the
comparator to become unbalanced. Both inputs are
disconnected once the conversion begins. The control logic and
charge redistribution DACs are used to add and subtract fixed
amounts of charge from the sampling capacitor arrays to bring
the comparator back into a balanced condition. When the
comparator is rebalanced, the conversion is complete. The
control logic generates the ADC’s output code. The output
impedances of the sources driving the V
must be matched; otherwise, the two inputs will have different
settling times, resulting in errors.
ADC TRANSFER FUNCTION
The output coding for the AD7933/AD7934 is either straight
binary or twos complement, depending on the status of the
CODING bit in the control register. The designed code
transitions occur at successive LSB values (i.e., 1 LSB, 2 LSBs,
and so on) and the LSB size is V
V
the AD7933/AD7934 for both straight binary and twos
complement output coding are shown in Figure 20 and Figure 21,
respectively.
V
V
REF
IN+
IN–
/4096 for the AD7934. The ideal transfer characteristics of
111...111
111...110
111...000
011...111
000...010
000...001
000...000
Figure 20. AD7933/AD7934 Ideal Transfer Characteristic
B
A
A
B
V
0V
REF
NOTE: V
SW1
SW2
with Straight Binary Output Coding
Figure 19. ADC Conversion Phase
1 LSB
C
C
S
S
REF
Preliminary Technical Data
IS EITHER V
ANALOG INPUT
SW3
1 LSB = V
1 LSB = V
REF
REF
COMPARATOR
/1024 for the AD7933 and
OR 2 × V
REF
REF
IN+
/4096 (AD7934)
/1024 (AD7933)
REF
and the V
+V
REF
CAPACITIVE
CAPACITIVE
–1 LSB
CONTROL
LOGIC
DAC
DAC
IN−
pins