Filter that minimizes in-band noise and maximizes detection sensitivity of exponentially-modulated signals

A method for reducing the phase noise, that limits the performance, of a precision oscillator having an oscillator output signal having an output frequency (F0) and comprising residual amplitude modulated (AM) noise and residual phase noise, said method comprising:

• feeding the oscillator output signal into a phase modulator wherein said phase modulator reduces the residual phase modulation on the oscillator output signal based upon a negative feedback signal to form a reduced residual phase modulated output signal;
• feeding said reduced residual phase modulated output signal into a linear-time invariant (LTI) filter which equally splits said reduced residual phase modulated output signal into two paths whose outputs are shifted by 180 degrees relative to each other and are summed, thereby notching out the oscillator output frequency (F0) and transforming only the reduced residual phase noise modulated portion of said oscillator output signal with reduced residual phase noise output, thereby forming an LTI output signal which forms a first input signal to a multiplier;
• using a 90 phase shifter to produce a phase shifted output of said oscillator output signal with reduced residual phase noise to form a second input signal to said multiplier;
• multiplying said first input signal with said second input signal in said multiplier so as to multiply said 90 degree shifted output of said oscillator output signal with said LTI output signal, thereby producing a baseband replica of the oscillator output signal with reduced phase modulation and then feeding said baseband replica of the oscillator output signal through amplification and compensation to form a negative feedback signal, said negative feedback signal being applied to said phase modulator to reduce the oscillator phase noise;
• and
• auto-tuning said LTI filter to continuously tune said LTI filter to the oscillator output signal frequency (F0).