Circuits > Oscillators and timers > Low Frequency Sinewave Generators
Low Frequency Sinewave Generators
The two circuits below illustrate generating low frequency sinewaves by shifting
the phase of the signal through an RC network so that oscillation occurs where
the total phase shift is 360 degrees. The transistor circuit on the right
produces a reasonable sinewave at the collector of the 3904 which is buffered by
the JFET to yield a low impedance output. The circuit gain is critical for low
distortion and you may need to adjust the 500 ohm resistor to achieve a stable
waveform with minimum distortion. The transistor circuit is not recommended for
practical applications due to the critical adjustments needed.
The op-amp based phase shift oscillator is much more stable than the single
transistor version since the gain can be set higher than needed to sustain
oscillation and the output is taken from the RC network which filters out most
of the harmonic distortion. The sinewave output from the RC network is buffered
and the amplitude restored by the second (top) op-amp which has gain of around
28dB. Frequency is around 600 Hz for RC values shown (7.5K and 0.1uF) and can be
reduced by proportionally increasing the network resistors (7.5K). The 7.5K
value at pin 2 of the op-amp controls the oscillator circuit gain and is
selected so that the output at pin 1 is slightly clipped at the positive and
negative peaks. The sinewave output at pin 7 is about 5 volts p-p using a 12
volt supply and appears very clean on a scope since the RC network filters out
most all distortion occurring at pin 1.
Low Frequency Sinewave Generators circuit
Title: Low Frequency Sinewave Generators
Source: unknown
Published on: 2007-07-21
Reads: 860
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