OP193FSZ Datasheet, PDF (17/20 Pages) Analog Devices – Precision, Micropower Operational Amplifiers

From the formulas, it can be seen that if the span trim is adjusted
before the zero trim, the two trims are not interactive, which
greatly simplifies the calibration procedure.
Calibration of the transmitter is simple. First, the slope of the
output current vs. temperature is calibrated by adjusting the
span trim, R7. A couple of iterations may be required to be sure
the slope is correct.
When the span trim has been adjusted, the zero trim can be
made. Adjusting the zero trim does not affect the gain.
The zero trim can be set at any known temperature by adjusting
R5 until the output current equals:
( ) I_OUT
=

∆I _FS
∆T_OPERATING

 ^TAMBIENT

− T_MIN
+ 4 mA
Table 7 shows the values of R6 required for various temperature
ranges.
Table 7. R6 Values vs. Temperature
Temp Range
0°C to 70°C
−40°C to +85°C
−55°C to +150°C
R6
10 kΩ
6.2 kΩ
3 kΩ
A MICROPOWER VOLTAGE CONTROLLED
OSCILLATOR
The OP293 CMOS analog switch forms the precision VCO of
Figure 36. This circuit provides triangle and square wave
outputs and draws only 50 μA from a single 5 V supply. A1 acts
as an integrator; S1 switches the charging current symmetrically
to yield positive and negative ramps. The integrator is bounded
by A2, which acts as a Schmitt trigger with a precise hysteresis
of 1.67 V, set by Resistor R5, Resistor R6, and Resistor R7, and
associated CMOS switches. The resulting output of A1 is a
triangle wave with upper and lower levels of 3.33 V and 1.67 V.
The output of A2 is a square wave with almost rail-to-rail swing.
With the components shown, frequency of operation is given by
the equation:
fOUT = VCONTROL V × 10 Hz/V
However, the frequency can easily be changed by varying C1.
The circuit operates well up to 500 Hz.
OP193/OP293
V_CONTROL
R1
200kΩ
R2
200kΩ
R3
100kΩ
C1
75nF
5V
5V
2_–
8
A1
1
1/2 OP293
3
+
4
R5
200kΩ
6
–
A2
1/2 OP293
5
+
SQUARE
OUT
7
R4
200kΩ
TRIANGLE
OUT
R8
200kΩ
R6
200kΩ
5V
R7
200kΩ
1 IN/OUT
2 OUT/IN
CD4066
S1
14
V_DD
5V
CONT 13
3 OUT/IN
S2
4 IN/OUT
CONT 12
IN/OUT 11
5 CONT
6 CONT
7
V_SS
OUT/IN 10
S3
OUT/IN 9 _5V
S4
IN/OUT 8
Figure 36. Micropower Voltage Controlled Oscillator
Rev. C | Page 17 of 20