A low-frequency, low-power voltage controlled oscillator (VCO) used as part of a single chip multi-channel telemetry system for biomedical applications is described. A VCO having high linearity, low harmonic content, and using little chip area is necessary to achieve fidelity of the telemetered signals without crosstalk. The circuit uses a conventional triangle wave VCO to drive a novel sine-shaping circuit that provides a signal with low harmonic content with no trimming. The circuit operates with a power supply from 2.4 to 3.3 volts and draws approximately 45 microamperes per VCO plus 25 microamperes for dedicated bias circuitry. The operating frequency can be changed over a 2:1 range with better than 0.5% of full-scale linearity. The center frequency is accurate to 5% over the entire supply voltage range. The VCO output is in the form of a current which allows for simple summing of the subcarriers. The IC is fabricated using the MOSIS 2-micron BiCMOS process.
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