REV. B

AD8515

–13–

Wien Bridge Oscillator

The circuit in Figure 7 can be used to generate a sine wave, one

of the most fundamental waveforms. Known as a Wien Bridge

oscillator, it has the advantage of requiring only one low power

amplifier. This is an important consideration, especially for battery-

operated applications where power consumption is a critical

issue. To keep the equations simple, the resistor and capacitor

values used are kept equal. For the oscillation to happen, two

conditions have to be met. First, there should be a zero phase

shift from the input to the output, which will happen at the

oscillation frequency of

F

RC

OSC

=

¥

1

210

10

p

Second, at this frequency, the ratio of VOUT to the voltage at

+input (Pin 3) has to be 3, which means that the ratio of

R11/R12 should be greater than 2.

AD8515

1

3

2

V–

V+

VCC

U10

C10

1nF

R13

1k

R11

2.05k

C9

1nF

R10

1k

R12

1k

VEE

Figure 7. Low Power Wien Bridge Oscillator

High frequency oscillators can be built with the AD8515 due to its

wide bandwidth. Using the values shown, an oscillation frequency of

130 kHz is created and is shown in Figure 8. If R11 is too low, the

oscillation might converge; if too large, the oscillation will diverge

TIME (2 s/DIV)

0

0

0

00

0

0000

0

000

0

0

0

0

0

0

Figure 8. Output of Wien Bridge Oscillator