AD797BRZ-REEL Analog Devices Inc, AD797BRZ-REEL Datasheet - Page 15

• Manufacturer Part Number: AD797BRZ-REEL
• Description: IC,Operational Amplifier,SINGLE,BIPOLAR,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD797BRZ-REEL

• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Slew Rate: 20 V/µs
• Gain Bandwidth Product: 110MHz
• -3db Bandwidth: 8MHz
• Current - Input Bias: 250nA
• Voltage - Input Offset: 10µV
• Current - Supply: 8.2mA
• Current - Output / Channel: 50mA
• Voltage - Supply, Single/dual (±): ±5 V ~ 15 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Output Type: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

DISTORTION REDUCTION
The AD797 has distortion performance (THD < −120 dB,
@ 20 kHz, 3 V rms, R
feedback amplifiers.
At higher gains and higher frequencies, THD increases due to a
reduction in loop gain. However, in contrast to most conven-
tional voltage feedback amplifiers, the AD797 provides two
effective means of reducing distortion as gain and frequency
are increased: cancellation of the distortion of the output stage
and gain bandwidth enhancement by decompensation. By
applying these techniques, gain bandwidth can be increased to
450 MHz at G = 1000, and distortion can be held to −100 dB at
20 kHz for G = 100.
The unique design of the AD797 provides cancellation of the
output stage’s distortion. To achieve this, a capacitance equal to
the effective compensation capacitance, usually 50 pF, is
connected between Pin 8 and the output (see C2 in Figure 44).
Use of this feature improves distortion performance when the
closed-loop gain is more than 10 or when frequencies of interest
are greater than 30 kHz.
Bandwidth enhancement via decompensation is achieved by
connecting a capacitor from Pin 8 to ground (see C1 in Figure 44).
Adding C1 results in subtracting from the value of the internal
compensation capacitance (50 pF), yielding a smaller effective
compensation capacitance and therefore a larger bandwidth.
CALIBRATION
TEKTRONIX
FIXTURE
HP2835
2×
NOTES
USE CIRCUIT BOARD WITH GROUND PLANE.
V
IN
226Ω
Figure 43. Settling Time Test Circuit
1µF
1kΩ
L
0.47µF
1kΩ
= 600 Ω) unequaled by most voltage
2
3
0.1µF
AD829
100Ω
–
+
2
3
4.26kΩ
A2
AD797
–
+
–V
4
A1
OSCILLOSCOPE
S
–V
PREAMP INPUT
TO TEKTRONIX
1kΩ
4
+V
7
S
S
+V
7
SECTION
S
1kΩ
6
20pF
0.47µF
1µF
6
7A26
250Ω
(VIA LESS THAN 1FT
50Ω COAXIAL CABLE)
1MΩ
0.1µF
2×
HP2835
51pF
20pF
Rev. H | Page 15 of 20
The benefits of adding C1 are evident for closed-loop gains
of ≥100. A maximum value of ≈33 pF at gains of ≥1000 is
recommended. At a gain of 1000, the bandwidth is 450 kHz.
Table 8 and Figure 45 summarize the performance of the
AD797 with distortion cancellation and decompensation.
Table 8. Recommended External Compensation for
Distortion Cancellation and Bandwidth Enhancement
Gain
10
100
1000
–100
–110
–120
Figure 45. Total Harmonic Distortion (THD) vs. Frequency @ 3 V rms
–80
–90
Figure 44. Recommended Connections for Distortion Cancellation
100
R1
(Ω)
909
1 k
10 k
NOISE LIMIT, G = +1000
NOISE LIMIT, G = +100
A/B
300
R2
(Ω)
100
10
10
R2
R2
and Bandwidth Enhancement
C1
(pF)
0
0
0
1k
2
3
2
3
FREQUENCY (Hz)
R1
R1
AD797
AD797
G = +1000
R
for Figure 44b
C2
(pF)
50
50
50
L
3k
= 600Ω
G = +1000
R
A
L
8
8
C1, SEE TABLE
C2 = 50pF – C1
= 10kΩ
50pF
3 dB
BW
6 MHz
1 MHz
110 kHz
10k
C2
C1
6
6
G = +100
R
L
= 600Ω
30k
C1
(pF)
0
15
33
G = +10
R
L
= 600Ω
100k
C2
(pF)
50
33
15
B
AD797
300k
0.01
0.003
0.001
0.0003
0.0001
3 dB
BW
6 MHz
1.5 MHz
450 kHz