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DivideByN (Divide by N)

Symbol

Available in ADS and RFDE

Parameters

Name

Description

Units

Default

FnomIn

Nominal input frequency

kHz

1.0

N

Divide number

None

11

Notes/Equations
  1. This model performs a divide-by-N function on either a baseband-input or a selected-carrier input frequency. The model operates in transient, harmonic balance, or circuit envelope simulation.
    In transient, all signals are considered baseband.
    In circuit envelope, the FnomIn parameter defines which analysis frequency to use. If the analysis frequency is not within 0.5/timestep, a warning is issued and 0 Hz will be used for the analysis frequency.
  2. The input impedance is infinite. The output impedance fixed at 1 Ohm. If the output is in baseband mode, then its open circuit voltage is equal to the phase of the divided signal in radians. This results in a sawtooth waveform for a CW input. A sawtooth is output (instead of a square wave) to allow for the calculation of the actual frequency from the slope and for the accurate detection of zero crossings without the sampling jitter that would be introduced by the fixed rate sampling of a square wave. If the output is not in baseband mode, then the open circuit voltage is a 1V complex sinusoid at the divided frequency. Whether or not the output is in baseband is determined, in Circuit Envelope mode, by determining the carrier frequency, possibly dc, that is closest to FnomIn; if none are close enough, a warning is issued.
  3. In non-baseband mode of operation, the divider works by directly extracting the phase of the complex input. The delay of DivideByN = max(timestep, N/(2 × Fin), where Fin is the actual analysis frequency corresponding to FnomIn.
    In baseband mode of operation, the period of the input is determined by detecting when the baseband signal rises through the 0.5V threshold. From this period information, the phase of the divided signal is calculated. For a more standard counter model, see the counter model under probes.
  4. Divider with an RF Carrier Input show examples of the divider operating with an RF carrier input: one divider outputs a baseband output; one divider outputs the divided frequency at the other carrier frequency. Note that N can be time varying in order to simulate the effect of a fractional-N divider. Output Waveforms shows the simulation results.

Divider with an RF Carrier Input

Output Waveforms
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