Datasheet
AD8099
Data Sheet
Rev. D | Page 20 of 28
FREQUENCY (MHz)
CLOSED-LOOP GAIN (dB)
–1
3000
04511-0-032
1
10
8
9
7
6
5
4
3
2
1
0
V
S
= ±5V
G = +2
R
LOAD
= 1k
SOIC PACKAGE
10 100 1000
R
F
= R
G
= 200
R
F
= R
G
= 250
R
F
= R
G
= 300
FREQUENCY (MHz)
CLOSED-LOOP GAIN (dB)
1
–1
10
9
8
7
6
5
4
3
2
1
0
10 100 1000 3000
04511-0-058
C
F
= 1pF
C
F
= 0.5pF
C
F
= 1.5pF
V
S
= ±5V
G = +2
R
LOAD
= 1k
SOIC PACKAGE
FREQUENCY (MHz)
CLOSED-LOOP GAIN (dB)
0
10000
04511-0-034
1
12
10
11
9
8
7
6
5
4
3
2
1
V
S
= ±5V
G = +2
R
LOAD
= 1k
SOIC PACKAGE
10 100 1000
R
S
= 0
R
S
= 50
R
S
= 20
1
8
4
7
5
3
6
2
AD8099
C5
0.1F
C
C
C
F
C1
C4
10F
C2
10F
C3
0.1F
R
C
R
F
R
G
R
S
R1
+V
S
–V
S
V
OU
T
SOIC PINOUT SHOWN
V
IN
DISABLE
04511-0-117
Figure 68. Frequency Response for Various Values of R
F
, C
F
, R
S
TOTAL OUTPUT NOISE CALCULATIONS AND DESIGN
To analyze the noise performance of an amplifier circuit, the
individual noise sources must be identified. Then determine if
the source has a significant contribution to overall noise perfor-
mance of the amplifier. To simplify the noise calculations, we
will work with noise spectral densities, rather than actual
voltages to leave bandwidth out of the expressions (noise
spectral density, which is generally expressed in nV/
Hz
, is
equivalent to the noise in a 1 Hz bandwidth).
The noise model shown in Figure 69 has six individual noise
sources: the Johnson noise of the three resistors, the op amp
voltage noise, and the current noise in each input of the
amplifier. Each noise source has its own contribution to the
noise at the output. Noise is generally specified RTI (referred to
input), but it is often simpler to calculate the noise referred to
the output (RTO) and then divide by the noise gain to obtain
the RTI noise.
All resistors have a Johnson noise of
(4kBTR)
, where k is
Boltzmann’s Constant (1.38 × 10
–23
J/K), T is the absolute
temperature in Kelvin, B is the bandwidth in Hz, and R is the
resistance in ohms. A simple relationship, which is easy to
remember, is that a 50 Ω resistor generates a Johnson noise of
1 nV
Hz
at 25C. The AD8099 amplifier has roughly the same
equivalent noise as a 50 Ω resistor.