OPA4820ID Datasheet, PDF (19/34 Pages) Texas Instruments – Quad, Unity-Gain Stable, Low-Noise, Voltage-Feedback Operational Amplifier

OPA4820
www.ti.com
SBOS317D − SEPTEMBER 2004 − REVISED AUGUST 2008
+5V
V_CM
0.1µF
1kΩ
1kΩ
1/4
OPA4820
1:2
50Ω
Source
16.7dB
Noise Figure
Gain = 8V/V
18dB
200Ω
200Ω
800Ω
800Ω
1/4
OPA4820
V_CM
500Ω
R_S
R_S
Dual ADC
1 of 2
C_L
Channels
500Ω
Figure 11. Single-Supply Differential ADC Driver (1 of 2 channels)
Video
Input
335Ω
402Ω
1/4
OPA4820
75Ω
High output current drive capability allows three
back−terminated 75Ω transmission lines to be simultaneously driven.
75Ω Transmission Line
75Ω
75Ω
75Ω
75Ω
75Ω
75Ω
V_OUT
V_OUT
V_OUT
Figure 12. Video Distribution Amplifier
SINGLE OP AMP DIFFERENTIAL AMPLIFIER
The voltage-feedback architecture of the OPA4820, with
its high common-mode rejection ratio (CMRR), will provide
exceptional performance in differential amplifier configura-
tions. Figure 13 shows a typical configuration. The starting
point for this design is the selection of the R_F value in the
range of 200Ω to 2kΩ. Lower values reduce the required
R_G, increasing the load on the V₂ source and on the
OPA4820 output. Higher values increase output noise as
well as the effects of parasitic board and device
capacitances. Following the selection of R_F, R_G must be
set to achieve the desired inverting gain for V₂. Remember
that the bandwidth will be set approximately by the gain
bandwidth product (GBP) divided by the noise gain
(1 + R_F/R_G). For accurate differential operation (that is,
good CMRR), the ratio R₂/R₁ must be set equal to R_F/R_G.
R₁
V₁
R_G
V₂
+5V
Power−supply decoupling not shown.
R₂
1/4
OPA4820
50Ω
V_O
=
R_F
R_G
(V₁
−
V₂)
R_F
when ^R2 = ^RF
R₁ R_G
−5V
Figure 13. High-Speed, Single Differential
Amplifier
19