The UBZR1 synthesizer has three voltage controlled oscillators. All three can feed the audio path. One of them can also be used as a low frequency oscillator for modulation purposes.
|Linear frequency modulation input||y||y|
|Hard synchronisation input||y||y|
|Hard synchronisation output||y|
|Ring Modulator circuit||y|
|Inverted Sawtooth wave form||y|
The VCO module consists of two parts:
The VCO is a classical transistor exponentiator, current controlled Miller integrator and a mono-flop controlled reset circuit.
At the wave shaper's core is a 1-transistor sawtooth triangle converter. Sine waves are generated by over-loading the LM 13700 transconductance amplifier, which is used in the VCA sub-circuit.
Rectangle waves are generated using a standard comparator design.
The wave shaper provides eight different wave forms
An 8 to 1 analog multiplexer selects the chosen waveform. The multiplexer is controlled by a 3-bit digital logic signal ("switch controller triplet").
The VCO has a final output stage as a voltage controlled amplifier (VCA). There are in fact two VCAs, which are feed with the same input by the wave selector, but their outputs can be used independently. This came in naturally as the LM 13700 contains two transconductance amplifiers. Hence, the VCO module has two current outputs. Current outputs allow for easy mixing into a simple resistor load.
The output currents depend exponentially on the control voltages.