A-110-4

Quadrature Thru Zero Voltage Controlled Oscillator

A-110-4 is a special audio VCO. The term "quadrature" means that the oscillator outputs sine and cosine waveforms simultaneously. The term "Thru-Zero" means that even "negative" frequencies are generated. But this a bit a misleading term as negative frequencies do not really exist. "Negative" means in this connection simply that the sine/cosine waves will stop when the linear control voltage reaches 0V and continue with the opposite direction as the linear control voltage becomes negative and vice versa.
The main advantage of the A-110-4 is that the design uses a sine/cosine core. The sine/cosine waves are not derived from other waveforms (e.g. sawtooth or triangle) by means of waveshaping. Rather the sine and cosine waves are the core of the VCO which results in very pure waves with a minimum of distortion and overtones.

• separate control sections for linear and exponential frequency control

• exponential control section:

o Exponential manual control (Xtune)
o Exponential CV input (1V/Oct)
o Exponential CV input with attenuator (XFM)

• linear control section:

o Linear manual control (LFrq)
o Linear CV input with attenuator (LFM)

• LED display for positive/negative frequencies
• sine and cosine output

http://www.doepfer.de/A1104.htm