Symmetric Noise Source

If a transistor junction operating in Zener breakdown is used as a noise source, the amplitude of the noise signal is asymmetric. This problem can be solved by using two transistors as two independent noise sources. One of these has a series resistor to earth, and the other has a series resistor to the supply line. Each of these noise sources produces an asymmetric noise voltage, with opposite asymmetry. If these two voltages are combined, the amplitude of the result will be symmetric.