SIMPLIS Parts

Voltage-Controlled Oscillator w/ 50% Duty Cycle

The Voltage Controlled Oscillator w/ 50% Duty Cycle models a VCO with a programmable ramp peak and valley voltages and a voltage-to-frequency gain. This block is speed-optimized for SIMPLIS simulations and can be used as a fixed frequency oscillator by connecting a constant DC voltage source to the frequency pin. The oscillator output ramp waveform is a triangle wave with a 50% duty cycle. This oscillator includes an ON/OFF control pin and outputs commonly used signals that include the following:

For a VCO with a programmable duty cycle, see the Voltage-Controlled Oscillator w/ Programmable Duty Cycle topic.

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Model Name:

Voltage-Controlled Oscillator w/ 50% Duty Cycle

Simulator:

This device is compatible with the SIMPLIS simulator.

Parts Selector Menu Location:

Analog Functions | Timing and Oscillators | Simple 50% Duty-Cycle Voltage-Controlled Oscillator (No sync.)

Symbol Library:

simplis_analog_functions.sxslb

Model File:

simplis_analog_functions.lb

Subcircuit Name:

SIMPLIS_VCO_BB

Symbols:

Multiple Selections:

Multiple devices can be selected and edited simultaneously.

Previous Version Compatibility

This symbol was introduced with version 8.0; however, the model and supporting files are available in version 7.20 as well. In versions prior to 7.20, the schematic will simulate, but you will not be able to edit the parameters with the dialog pictured in this topic.

For a version of the VCO compatible with versions prior to version 7.20, see the parts selector entry:

Obsolete | Analog Functions | Timing and Oscillators | Voltage-Controlled Oscillator w/ 50% Duty Cycle

Symbol Migration

Symbols placed on schematics in previous versions of SIMetrix/SIMPLIS can be automatically migrated to use the new symbols. The schematic tools menu Tools ▶ Migrate Schematic Symbols to Version 8.00 will invoke a routine which migrates the existing symbols to the new symbols. As this action makes substantial changes to the schematic, it is recommended that you save a backup copy of the schematic first.

I/O Table

The following table describes the pins on the VCO symbol.

Pin_Name

I/O

Function

Description

VF

I

Input voltage that controls the clock frequency.

\[ f_{CLK} = VF \times Gain \]
where $Gain$ is the clock frequency when VF = 1.0

OFF

I

On/Off control voltage for the oscillator, positive logic

Oscillator runs when OFF voltage signal is less than 2.0V.

  • Once the oscillator is running, it stops when the voltage at the OFF pin exceeds 3.0V.
  • Once the oscillator stops running, it restarts when the voltage at the OFF pin drops below 2.0V.

RTN

 

The circuit return for the VCO

The ground reference for this circuit

RAMP

O

Saw tooth ramp voltage output

This output allows you to probe the internal oscillator ramp voltage.

  • The ramp voltage frequency is the same as the clock frequency.
  • The slope of the ramp is linear for both the rising portion as well as the falling portion.

CLK

O

Digital logic output

Logic 0 => CLK = 0V
Logic 1 => CLK = 5V

The clock frequency is controlled by the VF input.

Editing the VCO

To configure the VCO, follow these steps:

  1. Double click the symbol on the schematic to open the editing dialog.
  2. Make the appropriate changes to the fields described in the table below the image.

Label Parameter Description

Gain

 The gain of the VCO is described in Hz/V.
A VCO with a Gain parameter value of 100k will oscillate at 100kHz when the VF pin voltage is 1V. When the VF pin is 5V the same VCO will oscillate at 500kHz.

Top of ramp voltage

 The peak of the ramp voltage

Bottom of ramp voltage

 The valley of the ramp voltage

Examples

The test circuit used to generate the waveform examples in the next section can be downloaded here: simplis 073 vco 50 duty.sxsch.

Waveforms

 
The waveforms shown below are for a test circuit with the following characteristics:

 

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