Current-Starved VCO

The principle of this VCO lies in control of the inverters supply, thus controlling the oscillation frequency of the inverter based ring oscillator.


I used 5 inverter stages in this design. The schematic is below

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Transistor sizes I used are shown below

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The design primarily consists of computing the required current based on the node capacitance in between the inverters, frequency of oscillation and setting properly the biasing resistor RPC0

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In this case the design was optimized for usage in the 1.2 GHz fixed frequency PLL.


Below is the Kvco parameter simulation plot

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Below is a zoomed plot with markers at +/- 10 MHz around the main frequency

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Now I can compute my Kvco as

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Below is a Phase Noise plot from PSS simulation

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Looks pretty noisy, but well, this is a ring oscillator based VCO, which is very compact from the layout point of view but too noisy.

I will perform later more work on minimization of the phase noise of ring based VCO.