Current Sensing Theremint Oscillator With PLL and Differential Full Quadrant Sine Output
Yet another attempt to design the best theremin oscillator ever, with PLL and current sensing.
- VCO is based on State Variable Filter with fully differential integrators.
- Full quadrant 0.5Vpp 1V differential voltage VCO outputs, allows to synthesize any other phases.
- Pure sine waveform 3Vpp drive signal for LC tank (less than -70dB harmonics)
- 4.5V power supply (draws about 20mA when driving LC tank with 10mA current)
- Stable amplitude for wide range of output frequencies (100KHz .. 2MHz)
I believe, it should be practically usable as a front-end for digital theremins.
LTSpice model to play with is available on GitHub (clone repository and open theremin_oscillator_bjt_pll_v01.asc)
The schematic is expected to be cheap, with PCB manufacturing and assembly using JLCPCB.
* about 60 BJTs, most of them should be matching pairs
* LMH6642 is used as LC tank drive buffer, can provide up to 75mA current, with close to R/R output voltage.
* MCP6121 is used as Control Voltage buffer
Simulation screenshots:
Antenna voltage and inductor current
Control voltage
Antenna voltage and inductor current when locked
Drive signal voltage and current when locked
https://github.com/fpga-theremin/sensors/raw/main/models/ltspice/theremin_oscillator_bjt_analog_pll/images/theremin_oscillator_bjt_pll_sim_drive_voltage_and_current_locked.png
Drive signal FFT in locked state
VCO differential output
