Frequency Selective Logarithmic Amplifier With Intrinsic Frequency Demodulation Capability

A system for use in a receive chain of a communication device, the system comprising:

• an amplifying circuit configured to receive an input signal and to generate an oscillation based on the input signal;
• one or more quadripole resonant circuits configured to establish a frequency pass band transfer response with a substantially zero phase region, the one or more quadripole resonant circuits coupled to the amplifying circuit and configured to establish a frequency of operation of the system;
• a sampling circuit coupled to the amplifying circuit and configured to terminate the oscillation based on a predetermined threshold so as to periodically clamp and restart the oscillation to generate a series of voltage spikes, where an instantaneous frequency of the voltage spikes carries FM and AM modulation information of the input signal and is output as a output signal, wherein the output signal has a different frequency than the input signal;
• a low pass filter circuit coupled between the amplifier circuit and the sampling circuit to isolate the output signal from the input signal and the oscillation generated by the amplifier;
• a matching circuit configured to receive at least one of the input signal or the output signal and to improve matching and coupling of one or more of the input signal or the output signal;
• and
• an isolation circuit between the input signal and the matching circuit, the isolation circuit configured to reduce leakage of backward energy.

A logarithmic detector amplifier for use in a receive chain of a communication device, the logarithmic detector amplifier comprising:

• an FM receiver configured to receive an FM input signal;
• an amplifier configured to receive an input signal and to generate an oscillation based on the FM input signal;
• at least one quadripole coupled to the amplifier, the at least one quadripole having a parallel resonance circuit and a series resonance circuit, the at least one quadripole configured as a bandpass filter to filter the FM input signal and to cause the amplifier to resonate at a target frequency;
• and
• a sampling circuit coupled to the amplifier and configured to terminate the oscillation based on a predetermined threshold so as to periodically clamp and restart the oscillation to generate a series of voltage spikes, wherein an instantaneous frequency of the voltage spikes carries FM modulation information of the FM input signal and is output as an FM output signal;
• wherein the target frequency is variable and based on at least one parameter of the logarithmic detector amplifier.

A system for use in a FM receiver in a super-heterodyne topology, the system comprising:

• a logarithmic detector amplifier (LDA) configured to receive a first intermediate signal at a first predetermined frequency, the LDA configured to generate an oscillation based on the first intermediate signal, determine modulation information from the oscillation, and generate a second intermediate signal at a second predetermined frequency;
• a first mixer configured to receive a radio frequency (RF) input signal at an input frequency and to convert the RF input signal to the first intermediate signal at the first predetermined frequency, wherein the input frequency within a range of frequencies;
• and
• a first variable oscillator configured to provide the first mixer with an indication of a difference between the input frequency and the first predetermined frequency.

A system for use in a receive chain of a communication device, the system comprising:

• an amplifying circuit configured to receive an input signal and to generate an oscillation based on the input signal;
• one or more parallel resonant circuits coupled to the amplifying circuit and configured to establish a frequency of operation of the system;
• a sampling circuit coupled to the amplifying circuit and configured to terminate the oscillation based on a predetermined threshold so as to periodically clamp and restart the oscillation to generate a series of voltage spikes, wherein an instantaneous frequency of the voltage spikes carries frequency modulation (FM) and amplitude modulation (AM) modulation information of the input signal and is output as a output signal, and wherein the output signal has a different frequency than the input signal;
• and
• a low pass filter circuit coupled between the amplifier circuit and the sampling circuit to isolate an output signal from the input signal and the oscillation generated by the amplifier;
• wherein the frequency of operation of the system is different than a frequency of the input signal such that input FM signal modulation can be demodulated on a slope of a frequency response of the system using slope detection.

A system for use in a receive chain of a communication device, the system comprising:

• an amplifying circuit configured to receive an input signal and to generate an oscillation based on the input signal;
• one or more parallel resonant circuits coupled to the amplifying circuit and configured to establish a frequency of operation of the system;
• a sampling circuit coupled to the amplifying circuit and configured to terminate the oscillation based on a predetermined threshold so as to periodically clamp and restart the oscillation to generate a series of voltage spikes, wherein instantaneous frequency of the voltage spikes carries frequency modulation (FM) and amplitude modulation (AM) modulation information of the input signal;
• a low pass filter circuit coupled between the amplifier circuit and the sampling circuit to isolate the output signal from the input signal and the oscillation generated by the amplifier;
• and
• a matching network followed by a low pass filter configured to output a demodulated FM signal from the input signal, wherein an input of the matching network is connected to one or more of the group consisting of an output of the amplifier, an input of the amplifier, a capacitor split within the one or more parallel resonant circuits, and wherein the output signal has a different frequency than the input signal;
• wherein the frequency of operation of the system is different than a frequency of the input signal such that input FM signal modulation can be demodulated on a slope of the frequency response of the system using slope detection.