1744 results about "Local oscillator signal" patented technology

Radio system including mixer device and switching circuit and method having switching signal feedback control for enhanced dynamic range and performance. Radio apparatus including: local oscillator input port for receiving periodic sinusoidal local oscillator signal; drive circuit for generating a substantially square-wave two-voltage level switching signal including: phase splitter circuit, voltage potential isolation circuit, and square wave signal generation circuit; FET mixing device; input / output signal separation circuit; analog-to-digital converter; and feedback control circuit. Radio tuner apparatus including low-band signal processing circuit; high-band signal processing circuit including first mixer circuit operating as an up-frequency converter, amplifier circuit, second mixer circuit operating as a down-frequency converter, and feedback control circuit for adjusting a duty cycle of a mixer switching device; signal combining circuit and output processing circuit. Method for operating radio system, apparatus, and tuner. Method of operating switching circuit.

A compensation circuit to correct for mismatch in a quadrature receiver comprises first and second mixers to receive a radio frequency (RF) modulated signal. One mixer receives an I local oscillator signal while the second mixer receives a Q local oscillator signal wherein the I and Q local oscillators have frequencies that are substantially identical. The output of the first and second mixers are coupled to first and second filters, respectively, which generate the I and Q output signals, respectively. Inherent circuit mismatch generate gain and / or phase errors that result in mismatch in the I and Q output signals. A correction circuit automatically applies a correction factor to at least one of the I and Q output signals to correct the gain and / or phase error by applying a multiplication factor to at least one of the I and Q output signals to thereby generate a corrected signal. The correction factors must be determined on a unit by unit basis. Testing in the final stages of factory assembly may be used to determine the value of the correction factor. The correction factor may be stored in a memory of the wireless communication device and used thereafter.

The present invention provides for a system and method for improvement of radio transmitter and receiver frequency accuracy for a local radio communication unit that communicates digital data with a remote communication unit. In the local unit the received radio signal is down-converted, and converted to complex baseband digital samples by an analog-to-digital converter. A downlink digital phase rotator applies a fine frequency shift to the samples in accordance with a receiver frequency offset command. The resultant baseband signal is used by the data demodulator and by a receiver frequency error estimator to obtain receiver frequency errors. A data modulator generates baseband complex samples which are shifted in carrier frequency by an integrated uplink digital phase rotator in accordance with a transmitter frequency offset command. The modulated samples are then converted by a digital-to-analog converter and upconverted in frequency for radio transmission to the remote unit. The local oscillator signals for both upconverter and downconverter are phase locked to a reference frequency generated by a VCXO. An automatic frequency control (AFC) function nulls the transmitter and receiver frequency error by the frequency adjustment commands to the uplink and downlink phase rotators or to the VCXO digital-to-analog converter (VCXO DAC) by feedback control principals based on measured receiver frequency error. During frequency track mode when communications between local and remote units are possible, the AFC only adjusts radio frequency via phase rotator commands and the VCXO command remains fixed, thereby avoiding communications performance degradation by VCXO frequency quantization error due to the VCXO DAC. The AFC adjusts VCXO frequency only during a preliminary acquisition mode prior to data communications, or to back out excessively large frequency offsets accumulated in the downlink and uplink phase rotators during track mode. When a VCXO adjustment is made in track mode, phase rotator adjustments are simultaneously applied to cancel the errors in transmitter and receiver radio frequencies caused by the step change due to VCXO frequency quantization thereby mitigating VCXO frequency quantization noise.