Pink Noise Generator


Pink Noise
Generator (Flicker Noise)

The circuit shown in fig. 1 is an implementation of a flicker
noise generator described in NBS technical note #604, "Efficient Numerical
and Analog Modeling of Flicker Noise Processes" by J.A. Barnes and Stephen
Jarvis, Jr. With the values shown the circuit will give a 1/f noise slope from
below one hertz to over four kilohertz. The circuit employs a TLC2272 op-amp
although other high impedance, low noise op-amps will work. The amplifier must
have low noise current since a farily high value resistor is used to generate
the 50 nV white noise; choose an op-amp with noise voltage less than 15 nV/root-Hz
and noise current less than 0.1 pA/root-Hz, both easily obtained with several
modern op-amps. The capacitor values vary slightly from the calculated values in
the referenced paper to simplify construction and the circuit includes bias to
allow the use of polarized electrolytic capacitors. The electrolytic capacitors
should be selected carefully since many aluminum electrolytics have poor
tolerances.

 Schematic

Unlike circuits employing zeners, reverse-biased transistors,
and other noisy devices, this circuit gives a predictable and repeatable output
level. Bringing the first op-amp’s output out through a 100uF capacitor in a
similar manner to the second will yield a handy, precise 5 uV/root-Hz white
noise covering the audio band that will serve as an excellent source for
calibrating audio noise measurements. In order to bias this capacitor at about
+2.5 volts you may wish to add about 30 megohms from +5 VDC to the positive
input of the first op-amp. If you use a tantalum capacitor, bias is not
necessary since tantalums can withstand zero bias. (F.Y.I.: Even a small reverse
bias voltage up to about 10% of the rating is OK with tantalum capacitors.) A
summing amplifier could be added to combine the white noise at the output of the
first op-amp to the flicker noise at the output to simulate various noisy
devices and systems. The two inputs to the summing amplifier would allow for
independent adjustment of the white and flicker components.


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