OPA699M Datasheet, PDF (21/32 Pages) Texas Instruments – GAIN +4 STABLE WIDEBAND VOLTAGE LIMITING AMPLIFIER

OPA699M
www.ti.com
SGLS289A – MAY 2005 – REVISED MARCH 2006
APPLICATION INFORMATION (continued)
LOW DISTORTION, LIMITED OUTPUT, ADC INPUT DRIVER
Figure 52 shows a simple ADC driver that operates on a single supply, and gives excellent distortion
performance. The limit voltages track the input range of the converter, completely protecting against input
overdrive. Note that the limiting voltages have been set 100 mV above/below the corresponding reference
voltage from the converter. This circuit also implements an improved distortion for an inverting gain of –2 using
external compensation.
V_S = +5V
V_H = +3.6V
0.1µF
1.4kΩ
V_S = +5V
3
7
OPA699 ^{8 6}
2
5
1.4kΩ
4
24.9Ω
0.1µF
IN
100pF
1000pF 374Ω
V_IN
18pF
750Ω
4pF
562Ω
102Ω
+3.5V
REFT
V_S = +5V
RSEL +V_S
ADS822
10-Bit
40MSPS
REFB
+1.5V
102Ω
INT/EXT GND
10-Bit
Data
V_L = +1.4V
0.1µF
562Ω
Figure 52. Single Supply, Limiting ADC Input Driver
S0038-02
LIMITED OUTPUT, DIFFERENTIAL ADC INPUT DRIVER
Figure 53 shows a differential ADC driver that takes advantage of the OPA699 limiters to protect the input of the
ADC. Two OPA699s are used. The first one is an inverting configuration at a gain of –2. The second one is in a
noninverting configuration at a gain of +2. See the Low Gain Compensation for Improved SFDR section for a
discussion of stability issues of the OPA699 operating at a gain less than four. Each amplifier is swinging 2 V_PP
providing a 4-V_PP differential signal to drive the input of the ADC. Limiters have been set 100 mV away from the
magnitude of each amplifier maximum signal to provide input protection for the ADC, while maintaining an
acceptable distortion level.
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