ADA4896-2ACP-EBZ AD [Analog Devices], ADA4896-2ACP-EBZ Datasheet - Page 23

• Manufacturer Part Number: ADA4896-2ACP-EBZ
• Description: 1 nV/?Hz, Low Power
• Manufacturer: AD [Analog Devices]

Data Sheet
ADA4896-2/ADA4897-1/ADA4897-2
The
Doppler path in the ultrasound application after the I/Q demod-
ulators of the AD9279. Doppler signals can be typically between
100 Hz to 100 kHz. The low noise floor and high dynamic range
of the
choices for processing weak Doppler signals.
The rail-to-rail output and the high output current drive of
the
candidates for the I-to-V converter, current summer, and ADC
driver.
Figure 55 shows an interconnection block diagram of all
eight channels of the AD9279. Two stages of the
amplifiers are used. The first stage performs an I-to-V conver-
sion and filters the high frequency content that results from
the demodulation process. The second stage of the
amplifiers is used to sum the output currents of multiple
devices, to provide gain, and to drive the
18-bit SAR ADC.
ADA4896-2/ADA4897-1/ADA4897-2
Figure 55. Using the
ADA4896-2/ADA4897-1/ADA4897-2
ADA4896-2/ADA4897-1/ADA4897-2
CHANNEL A
CHANNEL H
ADA4896-2/ADA4897-1/ADA4897-2
LNA
LNA
GENERATION
AD7982
in the Ultrasound System
4
LO
make them suitable
are used in the CW
make them excellent
Φ
Φ
Φ
Φ
ADA4896-2
device, an
ADA4896-2
as Filters, I-to-V Converters, Current Summers, and ADC Drivers After the I/Q Outputs of the
AD9279
AD9279
Rev. | Page 23 of 28
CWI+
CWI–
CWQ+
CWQ–
B
1.5V
1.5V
1.5V
1.5V
R
R
R
R
A
A
A
A
The output-referred noise of the CW signal path depends on
the LNA gain, the selection of the first stage summing amplifier,
and the value of R
is important to know the active low-pass filter (LPF) values R
R
all eight channels of a single
for R
single-pole LPF.
The gain of the I-to-V converter can be increased by increasing
the filter resistor, R
decrease the filter capacitor, C
limiting the magnitude of the gain is the output swing and drive
capability of the op amp selected for the I-to-V converter, in this
example, the ADA4896-2/ADA4897-1/ADA4897-2. Because
any amplifier has limited drive capability, a finite number of
channels can be summed.
FILT
, and C
R
C
C
R
R
C
C
R
FILT
FILT
FILT
FILT
FILT
FILT
FILT
FILT
FILT
ADA4896-2/
ADA4897-1/
ADA4897-2
ADA4896-2/
ADA4897-1/
ADA4897-2
, and 2.0 nF for C
ADA4896-2/ADA4897-1/ADA4897-2
FILT
, as shown as Figure 55. Typical filter values for
2.5V
2.5V
2.5V
2.5V
FILT
FILT
. To determine the output-referred noise, it
. To keep the corner frequency unchanged,
ADA4896-2/
ADA4897-1/
ADA4897-2
ADA4896-2/
ADA4897-1/
ADA4897-2
FILT
50Ω
50Ω
50Ω
50Ω
; these values implement a 100 kHz,
AD9279
FILT
, by the same factor. The factor
4nF
4nF
are 100 Ω for R
18-BIT ADC
18-BIT ADC
AD7982
AD7982
Q
I
A
AD9279
, 500 Ω
A
,