Datasheet

OPA698
17
SBOS258D
www.ti.com
LIMITED OUTPUT, DIFFERENTIAL ADC INPUT DRIVER
Figure 6 shows a differential ADC driver that takes advan-
tage of the OPA698 limiters to protect the input of the ADC.
Two OPA698s 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. 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 magni-
tude of each amplifier's maximum signal to provide input
protection for the ADC while maintaining an acceptable
distortion level.
PRECISION HALF WAVE RECTIFIER
Figure 7 shows a half wave rectifier with outstanding preci-
sion and speed. V
H
(pin 8) will default to a voltage between
3.1V and 3.8V if left open, while the negative limit is set to
ground.
OPA698
+5V
–5V
V
IN
= 1V
PP
200Ω 24.9Ω
1kΩ
1kΩ
0.01µF
10pF
10pF
0.01µF
24.9Ω
100Ω
100Ω
OPA698
+5V
–5V
200Ω
+1.1V
–1.1V
IN
V
CM
ADC
IN
+1.1V
4V
PP
–1.1V
200Ω
FIGURE 6. Single to Differential AC-Coupled, Output Limited ADC Driver.
OPA698
6
V
O
–V
S
= –5V
+V
S
= +5V
V
IN
2
3
4
7
8
5
402Ω402Ω
200Ω
NC
FIGURE 7. Precision Half Wave Rectifier.
The gain for the circuit in Figure 5 is set at +2. Figure 8 shows
a 100MHz sinewave amplifier, with a gain of +2 and rectified.
Time (2ns/div)
Output
Input
Output Voltage (V)
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
FIGURE 8. 100MHz Sinewave Rectified.
HIGH-SPEED FULL WAVE RECTIFIER
There are two methods shown here to build a high-speed full
wave rectifier with a limiting amplifier: use the half-wave
rectifier described previously with another amplifier to obtain
the full wave rectified, or use the input to set the limiting
voltage.