Passive FET Research Articles

Comprehensive Analysis of Distortion in the Passive FET Sample-and-Hold Circuit

Analysis simplified with circuit insights reveals the major sources of distortion in a passive FET-switch-based sampling circuit: 1) $R_{\mathrm{\scriptscriptstyle ON}}$ -modulation; 2) turn-OFF-time instant; and 3) signal-dependent charge-injection. Explicit expressions for second- and third-order distortions advance intuitive understanding of the processes of distortion. Circuit simulations and measurement results establish the accuracy of the analysis. Since the three sources of distortion each have a unique dependence on circuit parameters and the input signal frequency, a systematic method is shown to optimize an S/H circuit for least distortion.

A linearized amplifier using self-mixing feedback technique

A linearized amplifier using self-mixing feedback technique is presented to cancel out third-order intermodulation distortion (IMD3) terms. Second harmonic terms, which are generated by the self-mixing mixer between base and collector of a BJT amplifier, can be used as a source for IMD3 cancellation. The amplifier is based on a common emitter BJT amplifier with a passive FET mixer and an emitter follower for self-mixing feedback. The amplifier has been implemented with discrete transistors on an FR-4 PCB. Up to 16-dB IMD3 rejection has been achieved by the self-mixing feedback technique at 2GHz with peak output power of 20dBm.

Noise in Current-Commutating Passive FET Mixers

Noise in the mixer of zero-IF receivers can compromise the overall receiver sensitivity. The evolution of a passive CMOS mixer based on the knowledge of the physical mechanisms of noise in an active mixer is explained. Qualitative physical models that simply explain the frequency translation of both the flicker and white noise of different FETs in the mixer have been developed. Derived equations have been verified by simulations, and mixer optimization has been explained.

Second-Order Intermodulation in Current-Commutating Passive FET Mixers

Amplitude-modulation detection in the mixer plagues the performance of the zero-intermediate-frequency receiver by downconverting the envelope of amplitude modulated blockers to baseband where the desired channel is after downconversion. Simple equations based on physical mechanisms of second-order intermodulation generation have been derived which can predict the IIP2 of the current-driven passive mixer accurately. Derived equations have been verified by SPECTRE and SPECTRE-RF simulations, and mixer optimization has been explained.

Millimeter-wave MMIC single-pole-double-throw passive HEMT switches using impedance-transformation networks

This paper proposes a new design method for passive FET switches in the millimeter-wave (MMW) regime. In contrast to the conventional resonant-type switch design method, this passive FET switch circuit utilizes impedance transformation to compensate the drain-source capacitance effect for the off state at high frequencies. By means of this new design concept, a Q- and V-band monolithic-microwave integrated-circuit single-pole double-throw (SPDT) switches using a GaAs pseudomorphic high electron-mobility-transistor process are demonstrated. The Q-band SPDT switch has a measured isolation better than 30 dB for the off state and 2-dB insertion loss for the on state from 38 to 45 GHz, while the V-band switch also shows a measured isolation better than 30 dB for the off state and 4-dB insertion loss for the on state from 53 to 61 GHz. The obtained isolation performance using this design approach outmatches previously published FET switches in the MMW frequency range.

DC-20 GHz N*M passive switches

High-order, bidirectional, DC-20-GHz switch networks are discussed. Single-chip 1*2, 1*4, and 2*2 switch MMICs have been demonstrated. Multiple chips have been used to demonstrate 4*4 and 1*16 switches. The switches all use a combination of series and shunt passive FET switching elements. The 1*4 switch is made of a single stage of switching elements, rather than the usual two stages of 1*2 switches. The 2*2 switch is comprised of two stages of 1*2 switches. The multiple-chip 4*4 switch is made of four stages of 1*2 switches (using the 2*2 switch MMICs). Two stages of 1*4 switches are used to make the 1*16 switch. >