ADA4817-1 Analog Devices, ADA4817-1 Datasheet - Page 20

• Manufacturer Part Number: ADA4817-1
• Description: Low Noise, 1 GHz FastFET Op Amps
• Manufacturer: Analog Devices

Specifications of ADA4817-1

• -3db Bandwidth: 1.05GHz
• Slew Rate: 870V/µs
• Vos: 400µV
• Ib: 2pA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 4nV/rtHz
• Vcc-vee: 5V to 10V
• Isy Per Amplifier: 21mA
• Packages: CSP,SOIC

ADA4817-1/ADA4817-2
The pole in the loop transmission translates to a zero in the
noise gain of the amplifier, leading to an amplification of the
input voltage noise over frequency.
Table 9. RMS Noise Contributions of Photodiode Preamp
Contributor
R
VEN Amp
IEN Amp
F
45
40
35
30
25
20
15
10
–5
5
0
0.1
Figure 52. Photodiode Preamp Frequency Response
G = 63V/V
R
V
V
L
S
OUT
= 100Ω
= 10V
= 6V p-p
Expression
VEN
IEN
1
4
kT
×
×
R
FREQUENCY (MHz)
×
C
F
R
S
×
F
+
×
C
f
10
2
f
M
2
×
C
×
+
. 1
F
. 1
C
57
57
D
+
C
100
F
×
f
3
×
. 1
1000
57
Rev. A | Page 20 of 28
The loop transmission zero introduced by C
amplification. The noise gain bandwidth extends past the pre-
amp signal bandwidth and is eventually rolled off by the decreasing
loop gain of the amplifier. The current equivalent noise from the
inverting terminal is typically negligible for most applications.
The innovative architecture used in the ADA4817-1/ADA4817-2
makes balancing both inputs unnecessary, as opposed to traditional
FET input amplifiers. Therefore, minimizing the impedance
seen from the noninverting terminal to ground at all frequencies
is critical for optimal noise performance.
Integrating the square of the output voltage noise spectral density
over frequency and then taking the square root allows users
to obtain the total rms output noise of the preamp. Table 9
summarizes approximations for the amplifier and feedback
and source resistances. Noise components for an example
preamp with R
(bandwidth of about 6.4 MHz) are also listed.
RMS Noise with R
94 μV
777.5 μV
0.4 μV
783 μV (total)
F
= 50 kΩ, C
F
= 50 kΩ, C
S
= 30 pF, and C
S
= 30 pF, C
F
F
= 0.5 pF
limits the
F
= 0.5 pF