UBZR1 Voltage Controlled Oscillator Module

Chelys Lyra


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.

Functional Description

Each VCO has the following features

Features Specific to VCO1, VCO2 or VCO3

Linear frequency modulation input y y  
Hard synchronisation input   y y
Hard synchronisation output y    
Ring Modulator circuit   y  
Inverted Sawtooth wave form     y

How the VCOs are interconnected

VCO Module Building Blocks

UBZR1 VCO Building Blocks

The VCO module consists of two parts:

VCO Saw Tooth Generator

UBZR1 VCO Saw Tooth Generator

The VCO is a classical transistor exponentiator, current controlled Miller integrator and a mono-flop controlled reset circuit.

VCO Wave Shaper

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

VCO Wave Form Selector

An 8 to 1 analog multiplexer selects the chosen waveform. The multiplexer is controlled by a 3-bit digital logic signal ("switch controller triple").

VCO Built-In Voltage Controlled Amplifiers

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.

Performance Specs

Schematics as SVG (Scalable Vector Graphics)


VCO1 Block Schematics

VCO1 Pitch Summer Schematics

VCO1 Core Schematics

VCO1 Wave Form Shaper and Selector Schematics

VCO1 Audio VCA Schematics

VCO1 Ring Modulator Current Source Schematics


VCO2 Block Schematics

VCO2 Pitch Summer Schematics

VCO2 Core Schematics

VCO2 Wave Form Shaper and Selector Schematics

VCO2 Audio VCA Schematics

VCO2 Modulation VCA Schematics

VCO2 Ring Modulator Schematics


Last change: 2024-01-11
© 2002-2024 Dr. Thomas Redelberger redetho(a‍t)

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