Direct conversion receiver per-selection
AssigneeNEC Corporation
InventorNigel James Tolson
Life of this patent
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Abstract
A tunable voltage controlled bandpass filter for a direct conversion receiver. A phase locked loop uses the phase change imparted by the bandpass filter to local oscillator breakthrough from the mixer for a measure of frequency difference between input RF and local oscillator output. An error voltage derived from the measured phase change is applied as a tuning control to the bandpass filter. A sample and hold arrangement allows disconnection of the tuning circuit for power saving. The filter is suitable for implementation as an integral part of an ASIC receiver.
Claims16
A tunable pre-selector filter for a direct conversion receiver comprising a voltage controlled band pass filter, receiving an RF input and feeding the filtered RF from the voltage controlled band pass filter as an input to a mixer for mixing with an output of a local oscillator, the output of the local oscillator being fed also to a phase detector for comparison with a local oscillator output obtained as leakage from the mixer having passed through the voltage controlled band pass filter and an output from the phase detector applied through a loop filter as a control voltage to the voltage controlled band pass filter.
Dependencies are inferred from the claim text.