Rejection of rf interferers and noise in a wireless communications transceiver

Abstract

The invention provides a radio receiver or transceiver having one or more low noise amplifiers corresponding to one or more antenna inputs wherein one or more outputs of the one or more low noise amplifiers is/are combined at a single output current summing node, a tunable, shunt notch filter is coupled or connected to the summed output node that allows for the attenuation of a Tx blocker or interferer, an external blocker or interferer or an internal on-chip interferer.

What is claimed is: 
     
         1 . A radio receiver or transceiver, comprising:
 one or more low noise amplifiers corresponding to one or more antenna inputs, wherein one or more outputs of the one or more low noise amplifiers are combined at a single output current summing node;   a tunable, shunt notch filter coupled or connected to the single output current summing node that allows for the attenuation of a Tx blocker or interferer, an external blocker or interferer or an internal on-chip interferer.   
     
     
         2 . The radio receiver of  claim 1  wherein said one or more low noise amplifiers use a wideband, current output topology. 
     
     
         3 . The radio receiver of  claim 1  wherein said shunt notch filter has a series capacitance and a series inductance that give a frequency null in a current transfer function, the series capacitance in the notch filter being tunable to allow the null to be steered to the blocker and/or interferer. 
     
     
         4 . The radio receiver of  claim 1  wherein said shunt notch filter has a series capacitance and shunt inductance and capacitance that give both a frequency null and frequency peak in the current transfer function, both the series capacitance and the shunt capacitance in the notch filter being tunable to allow the null and peak to be steered to the blocker and/or interferer and desired signal, respectively. 
     
     
         5 . The radio receiver of  claim 1  where said shunt notch filter has a series capacitance and series inductance and shunt impedance and inductance approach that gives both two separate frequency nulls and a frequency peak in the current transfer function, both the series capacitance and the shunt capacitance in the notch filter being tunable to allow the nulls and peak to be steered to the blocker and/or interferer and desired signal, respectively. 
     
     
         6 . The radio receiver of  claim 1  wherein said shunt notch filter has a negative conductance cell to provide Q factor enhancement to filter components including inductors and/or capacitors in the shunt notch filter. 
     
     
         7 . The radio receiver of  claim 6  wherein said negative conductance cell includes a variable bias current and/or variable device size negative conductance generating transistors. 
     
     
         8 . The radio receiver of  claim 7  wherein said variable bias current includes switchable devices in a current source circuit. 
     
     
         9 . The radio receiver  claim 7  wherein said variable device size negative conductance generating transistors include separately switched RF devices. 
     
     
         10 . The radio receiver of  claim 6  wherein said negative conductance cell has transistors and includes a circuit that determines a voltage distribution across the transistors and outputs a DC signal corresponding to the voltage distribution. 
     
     
         11 . The radio receiver of  claim 1 , wherein a notch of said notch filter is set to the correct null and peak frequencies via a calibration algorithm that runs in a digital state machine or in a microprocessor. 
     
     
         12 . The radio receiver of  claim 1 , wherein said notch filter is adapted to be powered down when there is no unwanted Tx blocker or external interferer present. 
     
     
         13 . The radio receiver of  claim 1 , wherein said notch filter is adapted to be operateable at a lower supply current when the unwanted Tx blocker or external interferer present does not require maximum rejection thereby saving power consumption. 
     
     
         14 . The radio receiver of  claim 1 , wherein said notch filter is adapted to provide interferer rejection and also adapted to ensure the notch filter does not degrade the overall receiver linearity. 
     
     
         15 . The radio receiver of  claim 1 , wherein a low noise amplifier (LNA) is followed by a passive attenuator that allows for a gain of the LNA to be set in dependence upon a noise figure, a linearity, an impedance match and a gain while the overall pre-mixer gain is set to a value required by the complete system. 
     
     
         16 . A notch filter method of calibrating a receiver having an low noise amplifier (LNA.) and a tunable, shunt notch filter having a capacitor and a negative conductance cell, the method comprising:
 reading an on-chip available capacitor correction value and applying the on-chip available capacitor correction value to the capacitor control words (Cn, Cp) of the shunt notch filter;   setting a bias current and RF device width control words of the negative conductance cell to an initial value that ensures stable operation;   applying a calibration tone to a LNA input at the desired receive channel frequency and adjusting the Cp value until the notch response begins to peak in amplitude;   returning the test tone to the corresponding transmit frequency and adjusting the Cn value until the notch attenuation is at a maximum;   calculating a resultant notch rejection and polling a Vmonitor signal to determine if a voltage bias in a negative G block is optimum for circuit linearity; and   repeating the steps of reading, setting, applying, retuning and calculating to optimize both notch rejection and linearity.   
     
     
         17 . A notch filter method of calibrating a transmitter having a pre power amplifier (PPA), a frequency upconverter and, a tunable, shunt notch filter with a capacitor and a negative conductance cell, the method comprising:
 reading an on-chip available capacitor correction value and applying the on-chip available capacitor correction value to capacitor control words (Cn, Cp) of the shunt notch filter;   setting a bias current and RF device width control words of the negative conductance cell to an initial value that ensures stable operation;   applying a calibration tone via a frequency upconverter at the desired transmit channel frequency and adjusting the Cp value until a notch response begins to peak in amplitude;   retuning the test tone to the corresponding receive frequency and adjusting the Cn value until the notch attenuation is at a maximum;   calculating a resultant notch rejection and polling a Vmonitor signal to determine if the voltage bias in a negative G block is optimum for circuit linearity; and   repeating the steps of reading, setting, applying, retuning and calculating to optimize both notch rejection and linearity.