Abstract:
A microwave oscillator (10) includes an oscillator (12) having an output and a control port (44) and,a feedback circuit (20) disposed between the output and the control port (44). The feedback circuit (20) includes a modulated laser (30) having an input responsive to a portion (16) of a signal from the output of the oscillator (12), and a photo detector (34) having an input responsive to an output signal from the modulated laser (30) delayed (32) by a predetermined amount of time. A detector (28) has a first input responsive to the output of the photo detector (34), a second input responsive to a portion of the output signal from the oscillator (12) shifted (26) in phase to be in phase quadrature with the signal at the first input of the detector (28). The output of the detector (28) is coupled to the control port (44) of the oscillator (12). The output signal from the detector (28) is only zero when there is no difference between the phase shifted signal from the phase shifter (26) and the delayed signal from the photo detector (34).
Abstract:
5 n7 An oscillator (10) includes an amplifier (12) having an input and an output and a feedback circuit (14) disposed between the input and the output of the amplifier (12). The feedback circuit (14) includes a plurality of resonators (34) and a pair of switches (32,38). Each switch (32,38) includes a first port and multiple connectable ports, the multiple connectable ports of each switch (32,38) connected to a corresponding one of the plurality of resonators (34). The feedback circuit (14) further includes a voltage-controlled phase shifter (22) disposed in series with the switches (32,38). The oscillator (10) further includes a discriminator circuit (16), responsive to signals from the feedback circuit (14), for providing a control signal (52) to the voltage-controlled phase shifter (22) for degenerating low frequency noise within the oscillator (10). With such an arrangement, high Q low noise resonators can be switched in and out of the circuit thus providing improved phase noise performance at high power levels with the desirable frequency agility required for a microwave oscillator.