CALIFORNIA MICRO DEVICES
for calculating invariably results in a value larger than
optimum,
2 R
s
1
>
2 R
f
1
(4)
2.4 Power Supply Decoupling
CMV7101
The CMV7101 is not prone to oscillation without the use
of power supply decoupling capacitors, however to
minimize hum and noise pick-up, it is recommended that
the rails be bypassed with 0.01
µF
capacitors.
Typical Application
3.0 Low Power and Supply Voltage Single Rail Oscillator
Operational amplifiers have been used for years to generate
frequency stable oscillators, but the circuit shown in Figure
3 provides a stable frequency operating from a single supply
voltage and drawing a mere 300
µA.
For (R
1
+ R
2
)
÷
R
1
=
0.473, the period, T, of the oscillator is given by:
T = 2 R
f
C
1
(5)
Since the parasitic capacitance is bound to change
between the breadboard phase and the production printed
circuit board, we recommend the use of a gimmick
which is made by twisting two lengths (about a foot) of
insulated wire (such as AWG 24) that are bared at both
ends. The gimmick is soldered across R
f .
With the circuit in
operation, C
f
is adjusted by clipping short lengths until the
compensation is nominal. Then simply measure the
capacitance of the gimmick on an impedance bridge.
Where: R
f
is the feedback resistor, C
1
is the capacitor
The period is easily adjusted by varying R
f
. R
3
ensures that the
circuit will start on a single rail by forcing A
1
s output to the
positive rail. R
4
s value is not critical but should be a factor of
10 greater than the parallel combination of R
1
and R
2
.
The circuit lends itself to a variety of applications such as
battery operated toys where a LED is required to flash at a
periodic rate. The high output current of the CMV7101 assures
that the LED will have sufficient current to turn it on.
R1
= 0.473
R1 + R2
Figure 1.
Input Capacitance Compensation
2.3 Capacitive Load Considerations
The CMV7101 is capable of driving capacitive loads in excess
of 100 pF without oscillation. However, significant peaking
will result. The easiest way to minimize this problem is to
use an isolation resistor as shown in
Figure 2.
Figure 3.
Single Rail Oscillator
Figure 2.
Isolating a Capacitve Load
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3/00
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Tel: (408) 263-3214
Fax: (408) 263-7846
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7
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