AD9273BSVZ-50 Analog Devices Inc, AD9273BSVZ-50 Datasheet - Page 22

• Manufacturer Part Number: AD9273BSVZ-50
• Description: 12Bit 50 MSPS Octal ADC
• Manufacturer: Analog Devices Inc
• Type: Crosspoint Switchr

Specifications of AD9273BSVZ-50

• Resolution (bits): 12 b
• Sampling Rate (per Second): 50M
• Data Interface: Serial
• Voltage Supply Source: Single Supply
• Voltage - Supply: 1.7 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 100-TQFP Exposed Pad, 100-eTQFP, 100-HTQFP, 100-VQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9273
CHANNEL OVERVIEW
Each channel contains both a TGC signal path and a CW Doppler
signal path. Common to both signal paths, the LNA provides user-
adjustable input impedance termination. The CW Doppler path
includes a transconductance amplifier and a crosspoint switch.
The TGC path includes a differential X-AMP® VGA, an antialiasing
filter, and an ADC. Figure 38 shows a simplified block diagram
with external components.
The signal path is fully differential throughout to maximize signal
swing and reduce even-order distortion; however, the LNA is
designed to be driven from a single-ended signal source.
Low Noise Amplifier (LNA)
Good noise performance relies on a proprietary ultralow noise
LNA at the beginning of the signal chain, which minimizes the
noise contribution in the following VGA. Active impedance
control optimizes noise performance for applications that benefit
from input impedance matching.
A simplified schematic of the LNA is shown in Figure 39. LI-x is
capacitively coupled to the source. An on-chip bias generator
establishes dc input bias voltages of around 0.9 V and centers
the output common-mode levels at 1.5 V (AVDD2 divided by
2). A capacitor, C
capacitor, C
SWITCH
T/R
S
, is connected from the LG-x pin to ground.
C
S
Figure 39. Simplified LNA Schematic
LG
SWITCH
C
, of the same value as the input coupling
SH
LI-x
T/R
V
CM
C
V
S
O
+
C
SH
C
C
FB
FB
R
R
C
LG
FB1
FB2
R
R
LO-x
LOSW-x
LI-x
LG-x
FB1
FB2
Figure 38. Simplified Block Diagram of a Single Channel
V
O
–
LNA
15.6dB,
17.9dB,
21.3dB
V
CM
LOSW-x
LG-x
LO-x
C
LG
Rev. B | Page 22 of 48
INTERPOLATOR
ATTENUATOR
–42dB TO 0dB
g
m
GAIN
SWITCH
ARRAY
The LNA supports differential output voltages as high as
4.4 V p-p with positive and negative excursions of ±1.1 V from a
common-mode voltage of 1.5 V. The LNA differential gain sets
the maximum input signal before saturation. One of three gains
is set through the SPI. The corresponding full-scale input for
the gain settings of 6, 8, and 12 is 733 mV p-p, 550 mV p-p, and
367 mV p-p, respectively. Overload protection ensures quick
recovery time from large input voltages. Because the inputs are
capacitively coupled to a bias voltage near midsupply, very large
inputs can be handled without interacting with the ESD protection.
Low value feedback resistors and the current-driving capability
of the output stage allow the LNA to achieve a low input-referred
noise voltage of 1.26 nV/√Hz at a gain of 21.3 dB. This is achieved
with a current consumption of only 10 mA per channel (30 mW).
On-chip resistor matching results in precise single-ended gains,
which are critical for accurate impedance control. The use of a
fully differential topology and negative feedback minimizes
distortion. Low second-order harmonic distortion is particularly
important in second-order harmonic ultrasound imaging
applications. Differential signaling enables smaller swings at
each output, further reducing third-order distortion.
Recommendation
It is highly recommended that the LG-x pins form a Kelvin type
connection to the input or probe connection ground. Simply
connecting the LG pin to ground near the device may allow
differences in potential to be amplified through the LNA. This
generally shows up as a dc offset voltage that can vary from
channel to channel and part to part, depending on the
application and layout of the PCB (see Figure 38).
POSTAMP
21dB
24dB,
27dB,
30dB
FILTER
PIPELINE
ADC
AD9273
SERIAL
LVDS
CWD[7:0]+
CWD[7:0]–
DOUTx+
DOUTx–