Multi-element phased array transmitter with LO phase shifting and integrated power amplifier
A fully integrated CMOS multi-element phased-array transmitter (transmitter) includes, in part, on-chip power amplifiers (PA), with integrated output matching. The transmitter is adapted to be configured as a two-dimensional 2-by-2 array or as a one dimensional 1-by-4 array. The transmitter uses a two step up-conversion architecture with an IF frequency of 4.8 GHz. Double-quadrature architecture for the up-conversion stages attenuates the signal at image frequencies. The phase selectors in each transmitter path have independent access to all the phases of the VCO. The double quadrature architecture results in two sets of phase selectors for each path, one for the in-phase (I) and one for the quadrature phase (Q) of the LO signal. The phase selection is done in two stages, with the first stage determining the desired VCO differential phase pair and the next stage selecting the appropriate polarity. An on-chip Balun is used for differential to single-ended conversion.
1. An N-element phased-array transmitter, each element of the phased-array further comprising:
a pair of phase selectors each adapted to select one of an in-phase and a quadrature phase from a local oscillator signal and to supply the selected phases as output signals, wherein each phase of the local oscillator is selected from among M generated phases of the local oscillator; and
a pair of RF mixers each associated with a different one of the pair of phase selectors and each adapted to receive the output signals supplied by its associated phase selectors and to generate a corresponding pair of RF signals using IF signals;
a driver adapted to receive and process the generated RF signals supplied by the mixers;
an amplifier adapted to amplify the RF signal processed by the driver; and
a plurality of IF mixers adapted to receive in-phase and quadrature phase of a base band signal as well as divided-down phases of the local oscillator to generate the IF signals.
2. The N-element phased-array transmitter of claim 1 wherein each of the M generated phases of the local oscillator is a differential signal.
3. The N-element phased-array transmitter of claim 2 wherein the driver disposed in each element comprises two driving stages, each driving stage comprising:
a differential cascode amplifier;
a fixed capacitive load coupled to output terminals of the differential cascode amplifier; and
an inductive load coupled to output terminals of the differential cascode amplifier.
4. The N-element phased-array transmitter of claim 3 wherein each driving stage further comprises:
at least one variable capacitor coupled between the output terminals of its associated differential cascode amplifier and adapted to be switched on and off via a bit supplied by a control logic circuit disposed in the phased-array.
5. The N-element phased-array transmitter of claim 4 wherein the amplifier disposed in each element comprises first and second amplification stages, wherein each first amplification stage further comprises:
a cascode amplifier;
a resistor and a first capacitor coupled in series and forming a first signal path to an input terminal of the cascode amplifier;
a second capacitor coupled to the input terminal of the cascode amplifier via a second path;
a first transmission line having a first terminal coupled to an output terminal of the cascode amplifier;
a second transmission line having a first terminal coupled to the second terminal of the first transmission line, and a second terminal coupled to a first terminal of a third capacitor; and
a third transmission line having a first terminal coupled to the second terminal of the first transmission line; wherein a second terminal of the third transmission line is adapted to supply an output signal to an associated second amplification stage of the amplifier.
6. The N-element phased-array transmitter of claim 5 wherein each second amplification stage further comprises:
a cascode amplifier;
a resistor and a first capacitor coupled in series and forming a first signal path to an input terminal of the cascode amplifier;
a second capacitor coupled to the input terminal of the cascode amplifier via a second path;
a first transmission line having a first terminal coupled to an output terminal of the cascode amplifier;
a second transmission line having a first terminal coupled to the first terminal of the first transmission line;
a third transmission line having a first terminal coupled to the input terminal of the cascode amplifier; and
a third capacitor having a first terminal coupled to a second terminal of the third transmission line, and a second terminal coupled to supply voltage.
7. The N-element phased-array transmitter of claim 6 , wherein each element further comprises a Balun coupled between the amplifier and driver disposed therein.
8. The N-element phased-array transmitter of claim 2 further comprising:
a frequency divider block adapted to divide the frequency of the local oscillator signal and to supply divided-down phases of the local oscillator.
9. The N-element phased-array transmitter of claim 8 further comprising:
a shift register configured to receive input control signals and supply output control signals to the 2N phase selectors.
10. The N-element phased-array transmitter of claim 9 further comprising:
an M-phase oscillator adapted to generate the M phases of the local oscillator.
11. The N-element phased-array transmitter of claim 10 further comprising a phase-locked loop adapted to generate the M phases of the local oscillator, said phased-locked loop further comprising:
a voltage controlled oscillator;
a loop filter;
a charge pump;
a phase/frequency detector;
a divide-by-four circuit; and
a divide-by-sixty four circuit.
12. The N-element phased-array transmitter of claim 11 wherein said local oscillator signal has a frequency of 19.2 GHz adapted to be locked to a reference clock signal that has a frequency of 75 MHz.
13. The N-element phased-array transmitter of claim 12 wherein said RF signal has a frequency of 24 GHz and said IF signal has a frequency of 4.8 GHz.
14. The N-element phased-array transmitter of claim 1 wherein said N is equal to 4 and said M is equal to 16.
15. The N-element phased-array transmitter of claim 1 wherein said phased-array transmitter is formed on a single semiconductor substrate.