AD829 Analog Devices, AD829 Datasheet - Page 13

• Manufacturer Part Number: AD829
• Description: High Speed, Low Noise Video Op Amp
• Manufacturer: Analog Devices

Specifications of AD829

• -3db Bandwidth: 120MHz
• Slew Rate: 230V/µs
• Vos: 200µV
• Ib: 3.3µA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 1.7nV/rtHz
• Vcc-vee: 9V to 36V
• Isy Per Amplifier: 6.5mA
• Packages: DIP,LCC,SOIC

Data Sheet
supply voltages should be used. Figure 38 is a graphical extension
of Table 4, which shows the slew rate/gain trade-off for lower
closed-loop gains, when using the shunt compensation scheme.
CURRENT FEEDBACK COMPENSATION
Bipolar, nondegenerated, single-pole, and internally
compensated amplifiers have their bandwidths defined as
where:
f
I is the collector current of the input transistor.
Table 4. Component Selection for Shunt Compensation
Follower Gain
1
2
5
10
20
25
100
T
is the unity-gain bandwidth of the amplifier.
100
f
10
T
1
1
=
Figure 38. Value of C
2
π
r
e
1
C
C
Inverter Gain
−1
−4
−9
−19
−24
−99
COMP
COMP
=
2
COMP
NOISE GAIN
π
and Slew Rate vs. Noise Gain
kT
q
10
I
C
R1 (Ω)
Open
1 k
511
226
105
105
20
COMP
V
S
= ±15V
R2 (Ω)
100
1 k
2.0 k
2.05 k
2 k
2.49
2 k
SLEW RATE
C
0
5
1
0
0
0
0
100
LEAD
1k
100
10
(pF)
Rev. I | Page 13 of 20
C
68
25
7
3
0
0
0
COMP
(pF)
C
r
kT/q approximately equals 26 mV at 27°C.
Because both f
the dynamic behavior of an amplifier is limited. Because
then
This shows that the slew rate is only 0.314 V/µs for every mega-
hertz of bandwidth. The only way to increase the slew rate is to
increase the f
Unfortunately, an amplifier with a bandwidth of 10 MHz can
only slew at 3.1 V/µs, which is barely enough to provide a full
power bandwidth of 50 kHz.
The AD829 is especially suited to a form of current feedback
compensation that allows for the enhancement of both the full
power bandwidth and the slew rate of the amplifier. The voltage
gain from the inverting input pin to the compensation pin is
large; therefore, if a capacitance is inserted between these pins,
the bandwidth of the amplifier becomes a function of its feed-
back resistor and the capacitance. The slew rate of the amplifier
is now a function of its internal bias (2I) and the compensation
capacitance.
e
COMP
is the inverse of the transconductance of the input transistors.
Slew
Slew Rate (V/µs)
16
38
90
130
230
230
230
Slew
is the compensation capacitance.
f
T
Rate
Rate
T
, and that is difficult because of process limitations.
T
and slew rate are functions of the same variables,
=
= 4
C
COMP
2
π
I
kT
q
−3 dB Small Signal Bandwidth (MHz)
66
71
76
65
55
39
7.5
AD829