AD80066KRSZ(RevA) 데이터 시트보기 (PDF) - Analog Devices
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AD80066KRSZ Datasheet PDF : 20 Pages
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AD80066
ANALOG INPUTS—SHA MODE
Figure 19 shows the analog input configuration for the SHA
mode of operation. Figure 20 shows the internal timing for the
sampling switches. The input signal is sampled when CDSCLK2
transitions from high to low, opening S1. The voltage on the
OFFSET pin is also sampled on the falling edge of CDSCLK2,
when S2 opens. S3 is then closed, generating a differential
output voltage that represents the difference between the
sampled input voltage and the OFFSET voltage. The input
clamp is disabled during SHA mode operation.
INPUT SIGNAL
OPTIONAL DC OFFSET
(OR CONNECT TO GND)
VINA
OFFSET
VINB
AD80066
S1
S2 S3
2pF
CML
A
2pF
CML
CML
B
CML
VINC
CML
C
CML
VIND
CML
D
CML
Figure 19. SHA Mode Input Configuration (All Four Channels Are Identical)
CDSCLK2
S1, S2 CLOSED
S1, S2 OPEN
S1, S2 CLOSED
Q3
(INTERNAL)
S3 OPEN
S3 CLOSED
S3 CLOSED
Figure 20. SHA Mode Internal Switch Timing
Figure 21 shows how the OFFSET pin can be used in a CIS
application for coarse offset adjustment. Many CIS signals have
dc offsets ranging from several hundred millivolts to more than
1 V. By connecting the appropriate dc voltage to the OFFSET pin,
the large dc offset is removed from the CIS signal. Then, the
signal can be scaled using the PGA to maximize the dynamic
range of the ADC.
VINA
AD80066
SHA
A OFFSET
VINB
SHA
B OFFSET
VOLTAGE
REFERENCE
FROM CIS
MODULE
AVDD
R1
DC OFFSET
R2
VINC
OFFSET
0.1µF
SHA
C OFFSET
Figure 21. SHA Mode Used with External DC Offset
PROGRAMMABLE GAIN AMPLIFIERS (PGA)
The AD80066 uses one PGA for each channel. Each PGA has a
gain range from 1× (0 dB) to 5.8× (15.5 dB), adjustable in
64 steps. Figure 22 shows the PGA gain as a function of the
PGA register value. Although the gain curve is approximately
linear-in-dB, the gain in V/V varies nonlinearly with register
code, following the equation
Gain
=
1
+
4.9
5.9
⎡ 63 −
⎢⎣ 63
G
⎤
⎥⎦
where G is the decimal value of the gain register contents and
varies from 0 to 63.
15
5.9
12
5.0
9
4.0
6
3.0
3
2.0
0
1.0
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 63
PGA REGISTER VALUE (Decimal)
Figure 22. PGA Gain Transfer Function
Rev. A | Page 18 of 20
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