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器件3D模型￥ 31.703
AD8339ACPZ 数据手册 - ADI（亚德诺）
制造商:
ADI（亚德诺）
分类:
RF射频器件
封装:
LFCSP-40
描述:
ANALOG DEVICES AD8339ACPZ 芯片, 正交解调器
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AD8339ACPZ数据手册
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AD8339 Data Sheet
Rev. B | Page 20 of 36
To determine the input referred noise, it is important to know
the active low-pass filter (LPF) values R
FILT
and C
FILT
, shown in
Figure 53. Typical filter values for a single channel are 1.58 kΩ
for R
FILT
and 1 nF for C
FILT
; these values implement a 100 kHz
single-pole LPF. If two channels are summed, as is done on the
AD8339 evaluation board, the resistor value is halved (787 Ω)
and the capacitor value is doubled (2.2 nF), maintaining the
same pole frequency at twice the AD8339 current.
If the RF and LO are offset by 10 kHz, the demodulated signal is
10 kHz and is passed by the LPF. The single-channel mixing gain
from the RF input to the AD8021 output (for example, I1´, Q1´)
is approximately 1.7× (4.7 dB) for 1.58 kΩ and 1 nF, or 6 dB less
for filter values of 787 Ω and 2.2 nF (0.85× or −1.3 dB). The
noise contributed by the AD8339 is then 11 nV/√Hz × 1.7 or
~18.7 nV/√Hz at the AD8021 output. The combined noise of
the AD8021 and the 1.58 kΩ feedback resistor is 6.3 nV/√Hz, so
the total output referred noise is approximately 19.7 nV/√Hz.
This value can be adjusted by increasing the filter resistor while
maintaining the corner frequency, thereby increasing the gain.
The factor 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 AD8021.
The limitation on the number of channels summed is the drive
capability of the amplifier, as explained in detail in the Channel
Summing section.
MULTICHANNEL SUMMATION
Analog Beamforming
Beamforming, as applied to medical ultrasound, is defined as
the phase alignment and summation of signals generated from a
common source, but received at different times by a multielement
ultrasound transducer. Beamforming has two functions: it imparts
directivity to the transducer, enhancing its gain, and it defines a
focal point within the body from which the location of the
returning echo is derived. The primary application for the
AD8339 is in analog beamforming circuits for ultrasound.
06587-052
AD8339
AD8332, AD8334 LNA
OR AD8335 PREAMP
TRANSMITTER
TRANSDUCER
CLOCK DATA
T/R
SW
R
FB
2
2
2
2
2
Φ
Φ
I1
Q1
T/R
SW
R
FB
2
2
2
2
2
Φ
Φ
I2
Q2
T/R
SW
R
FB
2
2
2
2
2
Φ
Φ
I3
Q3
T/R
SW
R
FB
2
2
2
2
2
Φ
Φ
I4
Q4
SDI
CONTROLLER
QUADRATURE
DIVIDER
0°
90°
SYSTEM TIMING
C
FILT
R
FILT
ΣQ
AD7665 OR
AD7686
AD7665 OR
AD7686
16-BIT ADC
Q DATA
C
FILT
R
FILT
ΣI
AD8021
AD8021
16-BIT ADC
I DATA
Figure 53. Interconnection Block Diagram for the AD8339
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