ad797bn Analog Devices, Inc., ad797bn Datasheet - Page 14

• Manufacturer Part Number: ad797bn
• Description: Ultralow Distortion, Ultralow Noise Op Amp
• Manufacturer: Analog Devices, Inc.

AD797
Table 4. Values for Follower with Gain Circuit
Gain
2
2
10
20
>35
The I-to-V converter is a special case of the follower configu-
ration. When the AD797 is used in an I-to-V converter, for
example as a DAC buffer, the circuit of
used. The value of C
is greater than 33 pF, a 100 Ω series resistor is required.
A bypassed balancing resistor (R
minimize dc errors.
R1
1 kΩ
300 Ω
33.2 Ω
16.5 Ω
10 Ω
Figure 37. Alternative Voltage Follower Connection
*SEE TEXT
**Use Power Supply Bypassing Shown in
**Use Power Supply Bypassing Shown in Figure 35
R1
R
S
C
*
S
*
Figure 38. Low Noise Preamplifier
R2
1 kΩ
300 Ω
300 Ω
316 Ω
(G − 1) × 10 Ω
L
depends on the DAC and again, if C
2
3
2
3
AD797
AD797
C
R2
+V
–V
100Ω
C
+V
–V
L
7
4
L
7
4
S
S
S
S
S
and C
**
**
6
**
**
6
C
≈20 pF
≈10 pF
≈5 pF
L
Figure 39 should be
S
) can be included to
Figure 35
R
600Ω
L
Noise
(Excluding r )
3.0 nV/√Hz
1.8 nV/√Hz
1.2 nV/√Hz
1.0 nV/√Hz
0.98 nV/√Hz
L
S
Rev. E | Page 14 of 20
THE INVERTING CONFIGURATION
The inverting configuration (Figure 40) presents a low input
impedance, R1, to the source. For this reason, the goals of both
low noise and input buffering are at odds with one another.
Nonetheless, the excellent dynamics of the AD797 makes
it the preferred choice in many inverting applications, and
with careful selection of feedback resistors, the noise penalties
are minimal. Some examples are presented in Table 4 and
Figure 40.
Table 5. Values for Inverting Circuit
Gain
−1
−1
−10
C
*SEE TEXT
R1
1 kΩ
300 Ω
150 Ω
S
*SEE TEXT
*
**Use Power Supply Bypassing Shown in
**Use Power Supply Bypassing Shown in
R1
I
IN
R
Figure 40. Inverting Amplifier Connection
Figure 39. I-to-V Converter Connection
S
*
R
S
R2
1 kΩ
300 Ω
1500 Ω
*
20pF TO 120pF
2
3
2
3
C
L
AD797
AD797
R
+V
–V
+V
–V
1
7
4
7
4
S
S
S
S
R
2
C
≈20 pF
≈10 pF
≈5 pF
100Ω
L
**
**
**
**
6
6
Figure 35
Figure 35
Noise
(Excluding r )
3.0 nV/√Hz
1.8 nV/√Hz
1.8 nV/√Hz
600Ω
R
L
S