I/Q modulator and demodulator with wide instantaneous bandwidth and high local-oscillator-port-to-radio-frequency-port isolation
An improved quadrature modulator/demodulator (IQMD) may use two-phase quadrature local oscillator (LO) signal generation for generating 0° and 90° LO signals, and an anti-phase combiner/divider (at 0° and 180°) on the RF (radio frequency) port. The IQMD may include mixers (which may be double-balanced passive mixers) that function as downconverters when a signal is incident at their radio frequency (RF) ports, and function as upconverters when signals are incident on their intermediate frequency (IF) ports. Accordingly, the IQMD may function as an I/Q modulator by connecting digital-to-analog converters (DAC) to the differential I and Q ports, and/or it may also function as an I/Q demodulator by connecting analog-to-digital converters (ADC) to the differential I and Q ports.
1. An apparatus comprising:
a first circuit comprising a radio frequency (RF) port; and
a plurality of mixers comprising a first set of ports coupled to the first circuit, and further comprising a second set of ports, wherein the plurality of mixers are configured to:
operate as downconverters when signals are applied to the plurality of mixers at the first set of ports; and
operate as upconverters when signals are applied to the plurality of mixers at the second set of ports.
2. The apparatus of claim 1 , wherein the first circuit is configured to perform at least one of the following:
combine out-of-phase signals present on the first set of ports onto the RF port; or
terminate in-phase signals present on the first set of ports onto a load connected to the first circuit.
3. The apparatus of claim 2 , wherein the first circuit is configured to perform at least one of the following:
generate out-of-phase input signals at the second set of ports, based on an input signal applied to the RF port; or
generate a summed output signal at the RF port, based on out-of-phase output signals applied to the first set of ports.
4. The apparatus of claim 1 , wherein the first circuit further comprises:
a second port coupled to a respective first pair of mixer ports of the first set of ports; and
a third port coupled to a respective second pair of mixer port of the first set of ports;
wherein the first circuit is configured to perform at least one of the following:
generate a pair of out-of-phase input signals at the second port and the third port, in response to the RF port being excited by an input signal; or
generate a summed output signal at the RF port, in response to the second port and the third port being excited by a respective pair of out-of-phase output signals.
5. The apparatus of claim 4 , wherein the plurality of mixers comprise:
a first mixer comprising the first pair of mixer ports, and configured to perform at least one of the following:
downconvert a first out-of-phase input signal of the pair of out-of-phase input signals to a first pair of incoming baseband signals; or
upconvert a first pair of outgoing baseband signals to a first out-of-phase output signal of the pair of out-of-phase output signals.
6. The apparatus of claim 5 , wherein the plurality of mixers comprise:
a second mixer comprising the second pair of mixer ports, and configured to perform at least one of the following:
downconvert a second out-of-phase input signal of the pair of out-of-phase input signals to a second pair of incoming baseband signals; or
upconvert a second pair of outgoing baseband signals to a second out-of-phase output signal of the pair of out-of-phase output signals.
7. The apparatus of claim 1 , further comprising:
a local oscillator (LO) port configured to receive an LO signal;
wherein the plurality of mixers are configured to:
perform downconversion when operating as downconverters, based on the LO signal; and
perform upconversion when operating as upconverters, based on the LO signal.
8. The apparatus of claim 7 , further comprising:
a zero-phase power splitter coupled to the LO port and configured to receive the LO signal and derive a first LO signal and a second LO signal from the LO signal, wherein the first LO signal and the second LO signal are in phase with respect to each other;
wherein a first mixer of the plurality of mixers is configured to perform upconversion and downconversion based on the first LO signal; and
wherein a second mixer of the plurality of mixers is configured to perform upconversion and downconversion based on the second LO signal.
9. The apparatus of claim 7 , further comprising:
a phase shifter coupled to the LO port and configured to receive the LO signal an generate an in-phase LO signal and a quadrature LO signal based on the LO signal;
wherein a first mixer of the plurality of mixers and a second mixer of the plurality of mixers are each configured to perform upconversion and downconversion based on the in-phase LO signal and the quadrature LO signal.
10. The apparatus of claim 9 , further comprising:
a first zero-phase power splitter configured to receive the in-phase LO signal and derive a first in-phase LO signal and a second in-phase LO signal from the in-phase LO signal; and
a second zero-phase power splitter configured to receive the quadrature LO signal and derive a first quadrature LO signal and a second quadrature LO signal from the quadrature LO signal;
wherein the first mixer is configured to perform upconversion and downconversion using the first in-phase LO signal and the first quadrature LO signal; and
wherein the second mixer is configured to perform upconversion and downconversion using the second in-phase LO signal and the second quadrature LO signal.
11. The apparatus of claim 1 , wherein the plurality of mixers comprise double-balanced passive mixer circuits.
12. A method for processing signals, the method comprising:
receiving first signals at a radio frequency (RF) port and providing second signals at the RF port;
when receiving the first signals at the RF port:
generating out-of-phase input signals based on the received first signals, and applying the out-of-phase input signals to a first set of ports of a plurality of mixers; and
downconverting, by the plurality of mixers, the out-of-phase input signals to corresponding baseband signals; and
when providing the second signals at the RF port:
upconverting, by the plurality of mixers, outgoing baseband signals to corresponding out-of-phase output signals, and applying the out-of-phase output signals to the first set of ports; and
generating summed output signals based on the out-of-phase output signals, and providing the summed output signals as the second signals.
13. The method of claim 12 , wherein the out-of-phase input signals comprise a pair of out-of-phase input signals, and wherein downconverting by the plurality of mixers comprises:
downconverting, by a first mixer of the plurality of mixers, a first out-of-phase input signal of the pair of out-of-phase input signals to a first pair of incoming baseband signals of the corresponding baseband signals; and
downconverting, by a second mixer of the plurality of mixers, a second out-of-phase input signal of the pair of out-of-phase input signals to a second pair of incoming baseband signals of the corresponding baseband signals.
14. The method of claim 12 , wherein the corresponding out-of-phase output signals comprise a pair of out-of-phase output signals, and wherein upconverting by the plurality of mixers comprises:
upconverting, by a first mixer of the plurality of mixers, a first pair of outgoing baseband signals of the outgoing baseband signals to a first out-of-phase output signal of the pair of the pair of out-of-phase output signals; and
upconverting, by a second mixer of the plurality of mixers, a second pair of outgoing baseband signals of the outgoing baseband signals to a second out-of-phase output signal of the pair of the pair of out-of-phase output signals.
15. The method of claim 12 , further comprising:
generating a local oscillator (LO) signal; and
performing the downconverting and the upconverting based on the generated LO signal.
16. The method of claim 15 , further comprising:
deriving a first LO signal and a second LO signal from the LO signal, wherein the first LO signal and the second LO signal are in phase with respect to each other;
wherein performing the downconverting and the upconverting based on the generated LO signals comprises:
a first mixer of the plurality of mixers performing respective first portions of the downconverting and the upconverting based on the first LO signal; and
a second mixer of the plurality of mixers performing respective second portions of the downconverting and the upconverting based on the second LO signal.
17. A transceiver comprising:
a first modulator/demodulator (MODEM) circuit; and
a second MODEM circuit;
wherein each MODEM circuit of the first MODEM circuit and the second MODEM circuit comprises:
a first circuit comprising a radio frequency (RF) port; and
a plurality of mixers comprising a first set of ports coupled to the first circuit, and further comprising a second set of ports, wherein the plurality of mixers are configured to:
operate as downconverters when signals are applied to the plurality of mixers at the first set of ports; and
operate as upconverters when signals are applied to the plurality of mixers at the second set of ports.
18. The transceiver of claim 17 , wherein the first circuit is configured to perform at least one of the following:
combine out-of-phase signals present on the first set of ports onto the RF port; or
terminate in-phase signals present on the first set of ports onto a load connected to the first circuit.
19. The transceiver of claim 17 , wherein the first circuit is configured to perform at least one of the following:
generate out-of-phase input signals at the second set of ports, based on an input signal applied to the RF port; or
generate a summed output signal at the RF port, based on out-of-phase output signals applied to the first set of ports.
20. The transceiver of claim 17 , further comprising:
a plurality of digital-to-analog converters coupled to the first MODEM circuit and configured to provide unmodulated analog baseband signals to the first MODEM circuit for the first MODEM circuit to operate as a modulator; and
a plurality of analog-to-digital converters coupled to the second MODEM circuit and configured to receive demodulated analog baseband signals from the second MODEM circuit for the second MODEM circuit to operate as a demodulator.