參數(shù)資料
型號(hào): AD976ACR
廠商: ANALOG DEVICES INC
元件分類: ADC
英文描述: 16-Bit, 100 kSPS/200 kSPS BiCMOS A/D Converters
中文描述: 1-CH 16-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, PDSO28
封裝: SOIC-28
文件頁數(shù): 16/23頁
文件大小: 577K
代理商: AD976ACR
AD9761
–16–
REV. B
The differential circuit shown in Figure 37 provides the neces-
sary level-shifting required in a single supply system. In this
case, AVDD, which is the positive analog supply for both the
AD9761 and the op amp is also used to level-shift the differen-
tial output of the AD9761 to midsupply (i.e., AVDD/2).
C
OPT
200
1k
IOUTA
IOUTB
AD9761
R
LOAD
200
AD8042
500
R
LOAD
50
1k
AVDD
Figure 37. Single-Supply DC Differential Coupled
Circuit
SINGLE-ENDED UNBUFFERED VOLTAGE OUTPUT
Figure 38 shows the AD9761 configured to provide a unipolar
output range of approximately 0 V to 0.5 V since the nominal
full-scale current, I
OUTFS
, of 10 mA flows through an R
LOAD
of
50
. In the case of a doubly terminated low-pass filter, R
LOAD
represents the equivalent load resistance seen by IOUTA or
IOUTB. The unused output (IOUTA or IOUTB) can be con-
nected to ACOM directly or via a matching R
LOAD
. Different
values of I
OUTFS
and R
LOAD
can be selected as long as the posi-
tive compliance range is adhered to.
50
IOUTA
IOUTB
AD9761
50
I
OUTFS
= 10mA
V
=
0V TO 0.5V
Figure 38. 0 V to 0.5 V Unbuffered Voltage Output
DIFFERENTIAL, DC COUPLED OUTPUT
CONFIGURATION WITH LEVEL SHIFTING
Some applications may require the AD9761 differential outputs
to interface to a single supply quadrature upconverter. Although
most of these devices provide differential inputs, its common-
mode voltage range does not typically extend to ground. As a
result, the ground-referenced output signals shown in Figure 38
must be level shifted to within the specified common-mode
range of the single-supply quadrature upconverter. Figure 39
shows the addition of a resistor pull-up network which provides
the level shifting function. The use of matched resistor networks
will maintain maximum gain matching and minimum offset
performance between the I and Q channels. Note, the resistor
pull-up network will introduce approximately 6 dB of signal
attenuation.
50
**
IOUTA
IOUTB
AD9761
50
**
500
*
500
*
500
*
500
*
AVDD
V
IN+
V
IN
QUADRATURE
UPCONVERTER
*
OHMTEK TO MC-1603-5000D
**
OHMTEK TO MC-1603-1000D
Figure 39. Differential, DC Coupled Output Configuration
with Level-Shifting
POWER AND GROUNDING CONSIDERATIONS
In systems seeking to simultaneously achieve high speed and
high performance, the implementation and construction of the
printed circuit board design is often as important as the circuit
design. Proper RF techniques must be used in device selection;
placement and routing; and supply bypassing and grounding.
The evaluation board for the AD9761, which uses a four-layer
PC board, serves as a good example for the above mentioned
considerations. The evaluation board provides an illustration of
the recommended printed circuit board ground, power and
signal plane layout.
Proper grounding and decoupling should be a primary objective
in any high speed, high resolution system. The AD9761 features
separate analog and digital supply and ground pins to optimize
the management of analog and digital ground currents in a system.
In general, AVDD, the analog supply, should be decoupled to
ACOM, the analog common, as close to the chip as physically
possible. Similarly, DVDD, the digital supply should be decoupled
as closely as physically as possible to DCOM.
For those applications requiring a single 5 V or 3.3 V supply for
both the analog and digital supply, a clean analog supply may
be generated using the circuit shown in Figure 40. The circuit
consists of a differential LC filter with separate power supply
and return lines. Lower noise can be attained using low ESR
type electrolytic and tantalum capacitors.
0.1 F
CER.
10-22 F
TANT.
100 F
ELECT.
AVDD
ACOM
+
+
FERRITE
BEADS
5V OR 3V POWER
SUPPLY
TTL/CMOS
LOGIC
CIRCUITS
Figure 40. Differential LC Filter for Single 5 V or 3 V
Applications
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AD976ACRS 16-Bit, 100 kSPS/200 kSPS BiCMOS A/D Converters
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