AD8065ART-EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD8065ART-EBZ Datasheet PDF : 29 Pages
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AD8065/AD8066
Table 5. RMS Noise Contributions of Photodiode Preamp
Contributor
Expression
RF (×2)
2 × 4 kT × RF × f2 × 1.57
Amp to f1
VEN × f1
Amp (f2 – f1)
VEN ×
CS + C M + CF + 2CD ×
CF
f2 − f1
Amp to (past f2)
VEN ×
CS + CM + 2CD + CF ×
CF
f3 ×1.57
RMS Noise with RF = 50 kΩ, CS = 15 pF, CF = 2 pF
64.5 μV
2.4 μV
31 μV
260 μV
270 μV (Total)
RS1
VN
RG
RS2
VP
VCC
0.1μ F
1/2
AD8066
0.1μ F
VEE
RF = 500Ω
4.7μ F
4.7μ F
R1
500Ω
2.2pF
R2
500Ω
VCC
0.1μ F
AD8065
RF = 500Ω
VCC
0.1μ F
1/2
AD8066
4.7μF
R3
500Ω
R4
500Ω
0.1μ F
VEE
2.2pF
0.1μ F
4.7μF
VEE
Figure 60. High Speed Instrumentation Amplifier
4.7μF
VO
4.7μ F
HIGH SPEED JFET INPUT INSTRUMENTATION
AMPLIFIER
Figure 60 shows an example of a high speed instrumentation
amplifier with high input impedance using the
AD8065/AD8066. The dc transfer function is
VOUT
= (VN
−VP
)
⎜⎜⎝⎛1
+
1000
RG
⎟⎟⎠⎞
For G = +1, it is recommended that the feedback resistors for
the two preamps be set to a low value (for instance 50 Ω for
50 Ω source impedance). The bandwidth for G = +1 is 50 MHz.
For higher gains, the bandwidth is set by the preamp, equaling
( ) ( ) Inamp−3dB = fCR × RG / 2 × RF
Common-mode rejection of the in-amp is primarily
determined by the match of the resistor ratios R1:R2 to R3:R4.
It can be estimated
VO
VCM
=
(δ1− δ2)
(1+ δ1) δ2
The summing junction impedance for the preamps is equal to
RF || 0.5(RG). This is the value to be used for matching purposes.
Rev. J | Page 25 of 28
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