Automatic electronic load pull circuit for oscillators

A load pull circuit comprising:

• a) a monitoring device having a supply voltage port, a tuning voltage port and a RF input port;
• b) a device under test having a supply voltage port, a tuning voltage port and a RF output port that provides an output signal;
• c) a voltage controlled phase shifter means having a control port, a RF input port, and a monitoring port;
• d) a dc power supply connected to the tuning voltage port of the device under test;
• and
• e) the RF output port of the device under test connected to the RF input port of the voltage controlled phase shifter means, the supply voltage port of the device under test connected to the supply voltage port of the monitoring device, the monitoring port connected to the RF input port of the monitoring device, the voltage tuning port of the monitoring device connected to the control port of the voltage controlled phase shifter means for applying a control voltage to the voltage controlled phase shifter means, the voltage controlled phase shifter means changing the phase of the output signal in response to the control voltage.

A method of testing a device under test comprising:

• a) providing a monitoring device, a voltage controlled phase shifter and a dc power supply;
• b) connecting the device under test to the monitoring device, the voltage controlled phase shifter and the dc power supply;
• c) generating an output signal from the device under test;
• d) feeding the output signal to the voltage controlled phase shifter;
• e) generating a modified output signal by the voltage controlled phase shifter;
• f) feeding the modified output signal from the voltage controlled phase shifter to the monitoring device;
• g) generating a control voltage by the monitoring device;
• h) feeding the control voltage to the voltage controlled phase shifter;
• i) to vary the control voltage such that the phase of the output signal in the voltage controlled phase shifter is changed.