US 7,405,613 B2 · Differential slope demodulator for low-IF frequencies

Abstract

A circuit and method for differential slope demodulator circuit are shown that utilize amplitude stabilizing of a frequency modulated signal to obtain an amplitude stabilized signal. Also shown is bandpass filtering of the amplitude stabilized signal for a first frequency that is offset by a shift frequency below an intermediate frequency, to obtain a first filtered signal and bandpass filtering the amplitude stabilized signal for a second frequency that is offset by the shift frequency above the intermediate frequency, to obtain a second filtered signal. The circuit and method further operate by detecting an envelope of the first filtered signal to obtain a first envelope signal, detecting an envelope of the second filtered signal to obtain a second envelope signal, and differencing the first and second envelope signals to obtain a demodulated output signal.

A differential slope demodulator circuit, the circuit comprising:

an amplitude stabilizer having an input and an output;
a first filter having an input coupled to the output of the amplitude stabilizer and an output, where the first filter is tuned to a first frequency that is offset by a shift frequency below an intermediate frequency for the demodulator circuit;
a second filter having an input coupled to the output of the amplitude stabilizer and an output, where the second filter is tuned to a second frequency that is offset by the shift frequency above the intermediate frequency for the demodulator circuit;
a first envelope detector having an input coupled to the output of the first filter and an output;
a second envelope detector having an input coupled to the output of the second filter and an output;
and
a subtractor having a first input coupled to the output of the first envelope detector, a second input coupled to the output of the second envelope detector, and an output, and
wherein:
the amplitude stabilizer further comprises:
an I channel amplitude stabilizer having an input for receiving an I channel of the demodulator circuit and an output, and
a Q channel amplitude stabilizer having an input for receiving a Q channel of the demodulator circuit and an output;
the first filter further comprises a first poly-phase resonator having a first input coupled to the output of the I channel amplitude stabilizer and a second input coupled to the output of the Q channel amplitude stabilizer, first and second outputs, and a current input;
the second filter further comprises a second poly-phase resonator having a first input coupled to the output of the I channel amplitude stabilizer and a second input coupled to the output of the Q channel amplitude stabilizer, first and second outputs, and a current input;
the first envelope detector further comprises a first quadrature envelope detector having a first input coupled to the first output of the first poly-phase resonator, a second input coupled to the second output of the first poly-phase resonator, and an output coupled to the first input of the subtractor;
the second envelope detector further comprises a second quadrature envelope detector having a first input coupled to the first output of the second poly-phase resonator, a second input coupled to the second output of the second poly-phase resonator, and an output coupled to the second input of the subtractor;
a first current summer having a first input for receiving a current corresponding to the intermediate frequency, a second input for receiving a current corresponding to the shift frequency and an output coupled to the current input of the first filter, where the first current summer is configured to add the currents at the first and second inputs and output a sum current;
and
a second current summer having a first input for receiving the current corresponding to the intermediate frequency, a second input for receiving the current corresponding to the shift frequency and an output coupled to the current input of the second filter, where the second current summer is configured to subtract the current the second input from the current at the first input and output a difference current.

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Differential slope demodulator for low-IF frequencies

Life of this patent

Differential slope demodulator for low-IF frequencies

Life of this patent

Abstract

Claims9