RF receiver
A RF transmitter includes a phase-locked loop having an oscillator arranged to output an oscillator carrier and a power amplifier arranged to conduct a power amplifier current. The RF transmitter includes a phase shifter module between the phase-locked loop and the power amplifier arranged to introduce a phase shift between the oscillator carrier and a harmonic of the power amplifier current in order reduce a frequency shift of the oscillator carrier due to pushing and/or pulling.
1 . A RF transmitter comprising:
a phase-locked loop, comprising an oscillator arranged to output an oscillator carrier,
a power amplifier, arranged to conduct a power amplifier current,
a phase shifter module between the phase-locked loop and the power amplifier, arranged to introduce a phase shift between the oscillator carrier and a harmonic of the power amplifier current, in order reduce a frequency shift of the oscillator carrier due to pushing and/or pulling,
a computing unit, and
an oscillator frequency shift measurement unit,
wherein:
the power amplifier is arranged to be ramped-up during a calibration phase,
the phase shifter module is arranged so that during this calibration phase, the variable phase shift takes different values,
the measurement unit is arranged to measure the oscillator frequency shift against a load power for each value of the phase shift,
the computing unit is arranged to select the value of the phase shift minimizing a peak-peak oscillator frequency shift against the load power,
the measurement unit is the phase-locked loop and comprises a phase detector module and an additional module connected to an output of the phase detector module,
the additional module is arranged so as to compute the oscillator frequency shift,
the phase shifter module comprises several selectable delay cells, each delay cell comprising several inverters, and
a control module comprises:
a temperature sensor, and
a potentiometer comprising a p-output and a n-output,
wherein the temperature sensor is arranged to control the n-output and the p-output, and the n-output and the p-output is arranged to control fourth terminals of N-type and P-type transistors of the several inverters, respectively.
2 . The RF transmitter of claim 1 , comprising a divider connected to the output of the oscillator and being arranged to divide the frequency of the oscillator carrier by a number, the phase shifter module being between the divider and the power amplifier.
3 . The RF transmitter of claim 1 , the phase shift of the phase shifter module being a variable phase shift.
4 . The RF transmitter of claim 1 , the phase-locked loop being an all-digital phase-locked loop.
5 . The RF transmitter of claim 1 , each delay cell comprises back-to-back inverters so as to control the harmonic of the power amplifier current.
6 . The RF transmitter of claim 1 , the phase shifter module comprising the control module, arranged to control the fourth terminal of at least some transistors for temperature compensation.
7 . The RF transmitter of claim 1 , wherein as the power amplifier is ramped up and the measurement unit measures the frequency shift, the computing unit is arranged to build a frequency shift-signal envelope look-up table.
8 . The RF transmitter of claim 7 , wherein after the calibration phase, a predistortion signal based on said look-up table is added to an oscillator frequency control input, in order to reduce further the frequency shift of the oscillator carrier due to pushing and/or pulling.
9 . The RF transmitter of claim 1 , wherein the power amplifier comprises a power amplifier decoupling capacitor and a tank, the tank sharing a terminal with a terminal of the decoupling capacitor and having an impedance at the harmonic equal or higher than 100Ω in order to reduce or impede a flow of said harmonic current before it reaches the power amplifier decoupling capacitor.
10 . The RF transmitter of claim 1 , an inductor of the oscillator having an eight shape so as to reduce a magnetic coupling between the inductor and a balun of the power amplifier and/or a supply/ground line of the power amplifier, and/or wherein the distance between the oscillator and the balun of the power amplifier, is (are) arranged so as to reduce said magnetic coupling.