LMH6622 Datasheet, PDF (20/33 Pages) National Semiconductor (TI) – Dual Wideband, Low Noise, 160MHz, Operational Amplifiers

LMH6622
SNOS986E – DECEMBER 2001 – REVISED JULY 2014
9.3 Differential Analog-to-Digital Driver
LMH6622
+
-
+V_OUT/2
1:N
x
R_S
R_C
R_{F 500:}
R_IN
110:
TO ADC
R_{F 500:}
 ^VS
-
+
LMH6622
-V_OUT/2
Figure 37. Circuit for Differential A/D Driver
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The LMH6622 is a low noise, low distortion high speed operational amplifier. The LMH6622 comes in either
SOIC-8 or VSSOP-8 packages. Because two channels are available in each package the LMH6622 can be used
as a high dynamic range differential amplifier for the purpose of driving a high speed analog-to-digital converter.
Driving a 1 kΩ load, the differential amplifier of Figure 37 provides 20 dB gain, a flat frequency response up to 6
MHz, and harmonic distortion that is lower than 80 dBc. This circuit makes use of a transformer to convert a
single-ended signal to a differential signal. The input resistor R_IN is chosen by the following equation,
R_IN =
1
N²
R_S
(15)
The gain of this differential amplifier can be adjusted by R_C and R_F,
R_F
A_V = 2 _RC
(16)
See Figure 38 and Figure 39 below for plots related to the discussion of Figure 37.
24
22
20
18
16
14
12
10 VS = ±5.0V
8.0 A_V = +9
6.0 RC = 110Ω
4.0 RF = 500Ω
2.0 ^RL ^{= 1kΩ}
0.0
10k 100k 1M 10M
100
M
1G
FREQUENCY (Hz)
54n
52n
50n
48n
46n
44n
42n
40n
38n
36n
34n
32n
30n
100
V_S = ±5.0V
A_V = +9
R_C = 110Ω
R_F = 500Ω
R_L = 1kΩ
1k 10k 100k 1M 10M
FREQUENCY (Hz)
Figure 38. Frequency Response
Figure 39. Total Output Referred Noise Density
20
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