Systems and methods are disclosed for improved linearity performance of a mixer. An example mixer includes switching circuit elements configured to be switched on and switched off based at least partly on a local oscillator signal and capacitors including a respective capacitor in parallel with each of the switching elements. The mixer is configured to mix the input signal with the local oscillator signal to thereby frequency shift the input signal.

A FET based double balanced mixer (DBM) that exhibits good conversion gain and IIP3 values and provides improved linearity and wide bandwidth. In one embodiment, a first balun is configured to receive a local oscillator (LO) signal and generate two balanced LO signals that are coupled to two corresponding opposing nodes of a four-node FET ring. A second balun is configured to pass an RF signal on the unbalanced side. The FET ring includes at least four FETs connected as branches of a ring, with the source of each FET connected to the drain of a next FET in the ring. Each FET is preferably fabricated as, or configured as, a low threshold voltage device having its gate connected to its drain, which causes the FET to operate as a diode, but with the unique characteristic of having close to a zero turn-on voltage.

Examples of passive diode-based transmitter detuning circuits and low-voltage active diode-based and receiver detuning circuits are provided.

A reflective modulator comprises a coupler, two diodes and two DC block units. The coupler has an input end used to output an output signal, an output end used to output an output signal, a first load end connected to one of the diodes and a second load end connected to another one of the diodes. The DC block units connect between the diodes and the coupler for DC blocking. A message signal is selectively inputted to both of the two DC block units for operating the state of the two diodes. A BPSK modulator using the reflective modulator and a quadrature modulator using the BPSK modulator are also introduced.

A FET based double balanced mixer (DBM) that exhibits good conversion gain and IIP3 values and provides improved linearity and wide bandwidth. In one embodiment, a first balun is configured to receive a local oscillator (LO) signal and generate two balanced LO signals that are coupled to two corresponding opposing nodes of a four-node FET ring. A second balun is configured to pass an RF signal on the unbalanced side. The FET ring includes at least four FETs connected as branches of a ring, with the source of each FET connected to the drain of a next FET in the ring. Each FET is preferably fabricated as, or configured as, a low threshold voltage device having its gate connected to its drain, which causes the FET to operate as a diode, but with the unique characteristic of having close to a zero turn-on voltage.

A linear frequency converter or mixer design that utilizes linear time-varying devices and that avoids interaction between the local oscillator (LO) current and other signals inside the mixer, thus achieving high linearity and signal purity. This mixer also uses a LO frequency at least two times lower than conventional mixers, hence improving isolation between different system partitions. This class of mixer may not require a power supply.

Radio frequency (RF) mixer circuits having a complementary frequency multiplier module that requires no balun to multiply a lower frequency base oscillator signal to a higher frequency local oscillator (LO) signal, and which has a significantly reduced IC area compared to balun-based frequency multipliers. In one embodiment, the complementary frequency multiplier module includes a complementary pair of FETs controlled by an applied base oscillator signal. The complementary FETs are coupled to a common-gate FET amplifier and alternate becoming conductive in response to the base oscillator signal. The alternating switching of the complementary FETs in response to the opposing phases of the base oscillator signal cause the common-gate FET amplifier to output a higher frequency local oscillator (LO) signal. The LO signal is coupled to the LO input of a mixer or mixer core of a type suitable for use in conjunction with a frequency multiplier.

Mixers with improved linearity are disclosed. A diode or FET ring mixer is implemented with at least one parallel shunt element coupled with the ring mixer, the shunt element providing shunt to a diode or FET, for example, to reduce the effect of nonlinear or off resistance and/or capacitance. Linearity, isolation, symmetry, even order harmonics of the ring mixer, or any combination thereof can be improved as a result. The linearity of the ring mixer with parallel shunt resistors can be further improved by adding series resistors in the ring according to certain embodiments.

A FET based double balanced mixer (DBM) that exhibits good conversion gain and IIP3 values and provides improved linearity and wide bandwidth. In one embodiment, a first balun is configured to receive a local oscillator (LO) signal and generate two balanced LO signals that are coupled to two corresponding opposing nodes of a four-node FET ring. A second balun is configured to pass an RF signal on the unbalanced side. The FET ring includes at least four FETs connected as branches of a ring, with the source of each FET connected to the drain of a next FET in the ring. Each FET is preferably fabricated as, or configured as, a low threshold voltage device having its gate connected to its drain, which causes the FET to operate as a diode, but with the unique characteristic of having close to a zero turn-on voltage.