OP90AZ/883 AD [Analog Devices], OP90AZ/883 Datasheet - Page 9

• Manufacturer Part Number: OP90AZ/883
• Description: Precision Low-Voltage Micropower Operational Amplifier
• Manufacturer: AD [Analog Devices]

Single Op Amp Full-Wave Rectifier
Figure 7 shows a full-wave rectifier circuit that provides the
absolute value of input signals up to ±2.5 V even though operated
from a single 5 V supply. For negative inputs, the amplifier acts
as a unity-gain inverter. Positive signals force the op amp output
to ground. The 1N914 diode becomes reversed-biased and the
signal passes through R1 and R2 to the output. Since output
impedance is dependent on input polarity, load impedances
cause an asymmetric output. For constant load impedances, this
can be corrected by reducing R2. Varying or heavy loads can be
buffered by a second OP90. Figure 8 shows the output of the
full-wave rectifier with a 4 V
V
IN
HP5082-2800
10k
R1
REFERENCE
2mA MAX
+5V
–
2
3
+
p-p
V
IN
OP90FZ
, 10 Hz input signal.
+5V
5k
7
4
R2
10k
R2
6
R1
1M
R3
100k
1N914
D1
HP
5082-
2800
V
OUT
R3
4.7k
2
3
OP90EZ
80k
2-WIRE 4 mA TO 20 mA CURRENT TRANSMITTER
The current transmitter of Figure 9 provides an output of 4 mA
to 20 mA that is linearly proportional to the input voltage.
Linearity of the transmitter exceeds 0.004% and line rejection is
0.0005%/volt.
Biasing for the current transmitter is provided by the REF-02EZ.
The OP90EZ regulates the output current to satisfy the current
summation at the noninverting node:
For the values shown in Figure 9,
giving a full-scale output of 20 mA with a 100 mV input.
Adjustment of R2 will provide an offset trim and adjustment of
R1 will provide a gain trim. These trims do not interact since
the noninverting input of the OP90 is at virtual ground. The
Schottky diode, D1, prevents input voltage spikes from pulling
the noninverting input more than 300 mV below the inverting
input. Without the diode, such spikes could cause phase reversal of
the OP90 and possible latch-up of the transmitter. Compliance of
this circuit is from 10 V to 40 V. The voltage reference output
can provide up to 2 mA for transducer excitation.
R5
7
4
6
I
OUT
=
R4
100k
16V
100
6
IN
REF-02EZ
I
OUT
I
+ 4mA
OUT
4
=
=
R
1



2
6
100



16
V
2N1711
IN
R6
100
R
Ω
I
OUT
2
R



V
5
IN
V+
(10V TO 40V)
+
+
5
R
4
L
V R
R
mA
1
5



OP90