AD7934-6 Analog Devices, AD7934-6 Datasheet - Page 17

• Manufacturer Part Number: AD7934-6
• Description: 4-Channel, 625 kSPS, 12-Bit Parallel ADC with a Sequencer
• Manufacturer: Analog Devices

Specifications of AD7934-6

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 625kSPS
• Interface: Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: Uni (Vref),Uni (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: SOP

Figure 22 shows a graph of the THD vs. the analog input
frequency for various supplies, while sampling at 625 kHz with
an SCLK of 10 MHz. In this case, the source impedance is 10 Ω.
Figure 22. THD vs. Analog Input Frequency for Various Supply Voltages
Figure 21. THD vs. Source Impedance in Fully Differential Mode
–100
–100
–110
–120
Figure 20. THD vs. Source Impedance in Single-Ended Mode
–40
–45
–50
–55
–60
–65
–70
–75
–80
–85
–90
–60
–65
–70
–75
–80
–85
–90
–95
–50
–60
–70
–80
–90
10
10
0
F
F
F
RANGE = 0 TO V
IN
IN
SAMPLE
V
DD
= 50kHz
= 50kHz
100
= 3V
= 625kSPS
V
SINGLE-ENDED MODE
V
DIFFERENTIAL MODE
DD
DD
= 3V
= 5V/3V
200
REF
INPUT FREQUENCY (kHz)
V
SINGLE-ENDED MODE
DD
R
R
= 5V
300
SOURCE
SOURCE
V
DD
100
100
= 5V
400
(Ω)
(Ω)
V
500
V
DD
DD
= 3V
= 5V
600
700
1k
1k
Rev. B | Page 17 of 28
ANALOG INPUT CONFIGURATIONS
The AD7934-6 has software-selectable analog input configura-
tions. The user can choose either four single-ended inputs, two
fully differential pairs, or two pseudo differential pairs. The analog
input configuration is chosen by setting the MODE0/MODE1
bits in the internal control register (see Table 9).
Single-Ended Mode
The AD7934-6 can have four single-ended analog input
channels by setting the MODE0 and MODE1 bits in the control
register to 0. In applications where the signal source has a high
impedance, it is recommended to buffer the analog input before
applying it to the ADC. An op amp suitable for this function is
the AD8021. The analog input range of the AD7934-6 can be
programmed to be either 0 V to V
If the analog input signal to be sampled is bipolar, the internal
reference of the ADC can be used to externally bias up this
signal to make it the correct format for the ADC.
Figure 23 shows a typical connection diagram when operating
the ADC in single-ended mode. This diagram shows a bipolar
signal of amplitude ±1.25 V being preconditioned before it is
applied to the AD7934-6. In cases where the analog input
amplitude is ±2.5 V, the 3R resistor can be replaced with a
resistor of value R. The resultant voltage on the analog input of
the AD7934-6 is a signal ranging from 0 V to 5 V. In this case,
the 2 × V
Differential Mode
The AD7934-6 can have two differential analog input pairs by
setting the MODE0 and MODE1 bits in the control register to
0 and 1, respectively.
Differential signals have some benefits over single-ended
signals, including noise immunity based on the device’s
common-mode rejection, and improvements in distortion
performance. Figure 24 defines the fully differential analog
input of the AD7934-6.
+1.25V
–1.25V
*ADDITIONAL PINS OMITTED FOR CLARITY.
0V
REF
Figure 23. Single-Ended Mode Connection Diagram
mode can be used.
V
IN
3R
R
R
R
REF
+2.5V
, or 0 V to 2 × V
0V
V
V
IN
IN
0
3
AD7934-6*
AD7934-6
V
REFOUT
REF
.
0.47µF