Datasheet

OPA699
18
SBOS261D
www.ti.com
LIMITED OUTPUT, DIFFERENTIAL ADC INPUT DRIVER
Figure 7 shows a differential ADC driver that takes advan-
tage of the OPA699 limiters to protect the input of the ADC.
Two OPA699s are used. The first one is an inverting configu-
ration at a gain of –2. The second one is in a noninverting
configuration at a gain of +2. Refer to the section,
Low Gain
Compensation for Improved SFDR
, for a discussion of stabil-
ity issues of the OPA699 operating at a gain less than 4.
Each amplifier is swinging 2V
PP
providing a 4V
PP
differential
signal to drive the input of the ADC. Limiters have been set
100mV away from the magnitude of each amplifier maximum
signal to provide input protection for the ADC while maintain-
ing an acceptable distortion level.
PRECISION HALF WAVE RECTIFIER
Figure 8 shows a half wave rectifier with outstanding preci-
sion and speed. V
H
(pin 8) will default to a 3.5 typically if left
open, while the negative limit is set to ground.
The gain for the circuit in Figure 8 is set at +6. Figure 9 shows
input and output for ±0.5V 100MHz input.
VERY HIGH-SPEED SCHMITT TRIGGER
Figure 10 shows a very high-speed Schmitt Trigger. The
output levels are precisely defined, and the switching time is
exceptional. The output voltage swings between V
H
and V
L
.
OPA699
+5V
–5V
V
IN
= 200mV
PP
1kΩ 24.9Ω
1kΩ
1kΩ
0.01µF
10pF
10pF
0.01µF
24.9Ω
100Ω
100Ω
OPA699
+5V
–5V
900Ω
+1.1V
–1.1V
IN
V
CM
ADC
IN
+1.1V
4V
PP
–1.1V
100Ω
OPA699
6
V
O
V
O
= Open
–V
S
= –5V
+V
S
= +5V
V
IN
2
3
4
7
8
5
750Ω150Ω
75Ω
50Ω
Source
Time (5ns/div)
Output
Input
Input and Output Voltage (V)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
–0.5
–1.0
OPA699
R
2
402Ω
R
1
200Ω
R
3
200Ω
V
REF
V
OUT
V
H
V
L
+2V
–2V
V
IN
FIGURE 8. Precision Half-Wave Rectifier.
FIGURE 9. 100MHz Sinewave Rectified.
FIGURE 10. Very High-Speed Schmitt Trigger.
FIGURE 7. Single to Differential AC-Coupled, High Gain Output Limited ADC Driver.