Magnus Encyclopedia

The V page

See Voltage Controled Amplifier.

See Voltage Controled Filter.

See Voltage Controled Oscillator


Voltage Controled Amplifier
An device which acts like an linear amplifier but for which the gain may be changed with an applied control voltage. It is normally an 2-quadrant multiplier where the input signal is allowed to vary in both the positive and negative range. The control voltage is normally either linearly or exponentially dependent to the gain. The VCA can be realised in numerous ways in which OTA and Gilbert cells are common. The VCA is related to ringmodulators.

Voltage Controled Filter
An device which act like an line filter but for which the filter characteristics with one or more applied control voltage. The control voltage will normally follow an exponential frequency behaviour which normally is adjustable. There exists those VCFs which will react with linearly frequency with applied voltage. Some filters will allow for voltage control over the filters Q value, and some filters may even allow for voltage control over filter type (lowpass, bandpass, highpass)

Voltage Controled Oscillator
An device which will generate waveforms. The frequency of these waveforms can be controled with an applied control voltage. Normally is the frequency changed exponentially, but some change linearly with the control voltage. Some VCOs may allow for smaller linear modulations as well as for the exponential modulation. Usually is there a coarse tuning knob and sometimes also a fine tuning knob. Some VCOs have a rotary switch to select which base octave the VCO should be tuned to where as others may be widely sweept. VCOs may have diffrent waveforms. Common waveforms is square, PWM, triangle and sawtooth. Some VCOs will also have sine waveform. The PWM waveform migth have an additional input for CV controlable pulse width but some VCOs only allow for knob controled pulse width. Some VCOs migth be synced to an applied signal (often from a diffrent VCO), this is a way to lock the waveforms to each other so that they will at have a common phase at the sync time. Some VCOs migth be PLL locked to an applied signal, this way they will track the frequency of that signal. VCOs typhically have problems with frequency tracking, frequency range and temperature stabillity of it's frequency.

(C) 1997, 1998, 1999
Magnus Danielson <cfmd at bredband dot net>