Zero IF receiver employing, in quadrature related signal paths, amplifiers having substantially sinh.sup.-1 transfer characteristics
First Claim
1. A zero IF receiver comprising an input terminal for an input signal having a frequency proximate a center frequency, means coupled to the input terminal for down-converting said input signal in frequency relative to said center frequency to produce down-converted in-phase and quadrature-phase signals, first and second amplifiers fed by said down-converting means and having a substantially sin h-1 transfer characteristic, the in-phase and quadrature-phase signals produced by said down-converting means being applied to said first and second amplifiers, respectively, which produce first and second output signals corresponding substantially to the logarithm of the in-phase and quadrature-phase signals, and demodulating means, said demodulating means comprising means for determining an indication of amplitude of the input signal by selecting, as an estimate of the amplitude of the input signal within 3 db of the correct value, that one of the first and second output signals having the larger signal absolute value and means for deriving an indication of phase angle of the input signal from the difference between the first and second output signals.
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Abstract
A zero IF receiver which is capable of detecting short duration or CW signals and of operating over a large dynamic range includes an input terminal for receiving an input signal, a quadrature down-converter coupled to the input terminal for producing quadrature related, frequency down-converted signals in a pair of signal paths. These signal paths each include an amplifier having a substantially sinh-1 transfer characteristic so that the pair of signal paths produce substantially logarithmic quadrature related output signals which are coupled to a demodulator. The demodulator converts the quadrature related output signals into amplitude and frequency descriptions of the input signal relative to a center frequency of the receiver. The amplitude description is determined by selecting the one of the quadrature related output signals having the larger absolute value and applying an amplitude correction thereto. The frequency description is determined by forming an indication of the phase angle of the input signal from the difference between the quadrature related output signals, applying a phase correction thereto, and determining the rate of change of the corrected phase angle indication.
120 Citations
18 Claims
- 1. A zero IF receiver comprising an input terminal for an input signal having a frequency proximate a center frequency, means coupled to the input terminal for down-converting said input signal in frequency relative to said center frequency to produce down-converted in-phase and quadrature-phase signals, first and second amplifiers fed by said down-converting means and having a substantially sin h-1 transfer characteristic, the in-phase and quadrature-phase signals produced by said down-converting means being applied to said first and second amplifiers, respectively, which produce first and second output signals corresponding substantially to the logarithm of the in-phase and quadrature-phase signals, and demodulating means, said demodulating means comprising means for determining an indication of amplitude of the input signal by selecting, as an estimate of the amplitude of the input signal within 3 db of the correct value, that one of the first and second output signals having the larger signal absolute value and means for deriving an indication of phase angle of the input signal from the difference between the first and second output signals.
Specification