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# VCO (Voltage Controlled Oscillator)

## VCO (Voltage Controlled Oscillator)

##### Parameters

Name

Description

Units

Default

Kv

Frequency tuning sensitivity (Hz/Volt)

kHz

1

Freq

Fundamental frequency

GHz

1

P

Power into Rout Load at Fundamental Frequency, complex value

None

−j × dbmtow(0)

Rout

Output resistance

Ohm

50

Delay

Transit time delay added to input tuning voltage

None

timestep

Harmonics

Ratio of harmonic voltage to fundamental voltage, complex value

None

list(-0.01, 0.002)

##### Notes/Equations
1. This is a simple VCO model that outputs a signal whose frequency is controlled in a linear manner by the input tuning voltage. The center frequency is defined by the Freq parameter, which references one of the analysis frequencies. A Freq value of 0 references dc and so defines the VCO as a baseband source; the output frequency is the baseband input voltage times the Kv parameter value. Only the baseband portion of the input tuning voltage is used to determine the VCO frequency offset.
2. The phase of the VCO output is clamped when time equals 0, so this model only functions as a VCO in the time-domain analysis modes, including circuit envelope and transient simulation. In a transient simulation, the VCO Freq parameter can be 0, or set to a value that is the VCO's nominal frequency.
3. The output resistance at all frequencies is set by Rout, which is internally limited to a minimum value of 0.1 Ohm. The VCO's fundamental output power into an Rout load is defined by the P parameter. The relative level, in linear units, of the second and third harmonics are defined by the Harmonics parameter; this parameter can be complex to allow definition of the relative phase of these harmonics. The initial phase for the fundamental frequency output is set to −90 degrees so that a sine waveform is created in baseband mode.
4. A Delay parameter value can also be specified for this VCO model. This puts an additional transit delay between the input tuning voltage and the actual change in the output frequency. A delay of at least one time-step does sometimes result in faster simulation speeds, and can be used to model the time delay inherent in any real VCO.
Care should be taken when using the VCO in baseband mode (Freq = 0). If the input voltage is allowed to go negative, the model will generate a negative frequency, and the waveform shape due to the harmonic content will be reversed.
The VCO_DivideByN model also allows the definition of a nonlinear frequency tuning characteristic.
5. The following figure shows the use of the VCO in an envelope simulation. The VCO is defined with significant second and third harmonic levels. Simulation results are shown in the next figure.

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