K. Krishnamurthy

Broadband GaAs MESFET and GaN HEMT resistive feedback power amplifiers

We report 0.2 to 6-GHz MMIC power amplifiers with 12-dB gain, over 23-dBm output power, and more than 25% power-added efficiency (PAE) in a GaAs MESFET technology offering 18 GHz f/sub /spl tau// and 12-V breakdown. These circuits have gain-bandwidth products of /spl sim/1.3/spl middot/f/sub /spl tau// and are more efficient than distributed power amplifiers. A first demonstration of similar circuits in GaN/AlGaN HEMT technology yielded 11-dB gain, 0.2 to 7.5-GHz bandwidth amplifiers with over 31.5-dBm output power and up to 15% PAE. With improved devices and models we expect significantly higher power from the GaN HEMT circuits.

Dual-gate AlGaN/GaN modulation-doped field-effect transistors with cut-off frequencies f/sub T/>60 GHz

We demonstrate dual-gate AlGaN/GaN modulation-doped field-effect transistors (MODFETs) with gate-lengths of 0.16 /spl mu/m and 0.35 /spl mu/m for the first and second gates, respectively. The dual-gate device exhibits a current-gain cut-off frequency f/sub T/>60 GHz, and can simultaneously achieve a high breakdown voltage of >+100 V. In comparison to single-gate devices with the same gate length 0.16 /spl mu/m, dual-gate FETs can significantly increase breakdown voltages, largely increasing the maximum allowable drain bias for high power application. The continuous wave (CW) output power is in excess of 3.5 W/mm at 8.2 GHz. The corresponding large-signal gain is 12 dB and the power added efficiency is 45%. The dual-gate device with different gate lengths shows the capability of providing simultaneous high cut-off frequencies, and high breakdown voltages for broadband power amplifiers.

Broad-band microwave power amplifiers in GaN technology

We report lumped power amplifiers with >4.4 W saturated output power over 2-8 GHz bandwidth in a GaN HEMT technology. Peak output power and PAE are 5.12 W and 21% respectively at 6 GHz, under class-A operation. Also reported are GaAs MESFET/GaN HEMT cascode distributed amplifiers with 1-9 GHz bandwidth and with peak output power and PAE of 1.35 W and 14% respectively at 8 GHz.

Cascode-delay-matched distributed amplifiers for efficient broadband microwave power amplification

We present a broadband distributed power amplifier topology capable of providing efficiencies approaching 50%. Unlike tapered-drain-line power TWAs, high-Z/sub 0/ lines are not required, greatly improving realizability in MMIC implementation. An experimental hybrid achieved bandwidth 25% of f/sub /spl tau// with /spl sim/15 dB gain and 30/spl plusmn/5% power-added-efficiency.

40 Gb/s TDM system using InP HBT IC technology

A 40 Gb/s time-division-multiplexing (TDM) system transmitter and receiver with 4-channel 10 Gb/s interface is presented. InP DHBT IC technology is used to implement the complete chipset (4:1 multiplexer with VCO /clock multiplication unit, modulator driver, transimpedance amplifier, limiting amplifier and 1:4 demultiplexer with clock and data recovery). A 2.26 km long transmission experiment was performed using the system with 40 Gb/s, 2/sup 31/, NRZ PRBS. The transmit eye exhibits a high extinction ratio >12.5 dB with 1 ps added RMS jitter and 4 dbm output power. Receive sensitivity is better than -7.8 dBm with 0.22 dB dispersion penalty.

43 Gb/s decision circuits in InP DHBT technology

Packaged master-slave D-flip-flops designed in InP DHBT technology with 150 GHz f/sub t/ and 180 GHz f/sub max/ are presented. Measurement results using a 43.2 Gb/s nonreturn to zero (NRZ), pseudo random binary sequence (PRBS) data (generated from 4 channels of 10.8 Gb/s, 2/sup 31/-1, PRBS data) and a 43.2 GHz clock, show a clock phase margin of 190/spl deg/. 2:1 Static frequency dividers designed using the D-flip-flops have been tested up to 50 GHz and show normal operation. These circuits are key building blocks in numerous front-end circuits used for 40 Gb/s optical communication systems.

A >25% PAE 0.2-6 GHz lumped power amplifier in a 18 GHz MESFET technology

We report 0.2-6 GHz MMIC power amplifiers with 12 dB gain, over 23 dBm output power and more than 25% power-added-efficiency in a GaAs MESFET technology offering 18 GHz f/sub /spl tau// and 12 V breakdown. These circuits have pain-bandwidth products of /spl sim/1.3 f/sub /spl tau// and are more efficient than distributed power amplifiers. These circuit topologies are being used in GaN based broad-band high power amplifiers in development.

High gain 40 Gb/s InP HBT drivers for EO/EA modulators

Single chip high gain InP HBT modulator drivers for 40 Gb/S systems are presented. With 30 dB gain, 41 GHz bandwidth and 6Vp-p differential output, the need for external pre-amplifiers and bias networks are eliminated. Transmitter performance with EO/EA modulators are evaluated.

40 Gb/s TDM SYSTEM TRANSCEIVER PROTOTYPE IN InP HBT TECHNOLOGY

A time-division-multiplexing (TDM) system transceiver with 4–channel 10 Gb/s interfaces to achieve 40 Gb/s non-return to zero (NRZ) transmission is presented. The front-end components are implemented in an indium phosphide double hetero-junction bipolar transistor (InP DHBT) technology. They include a 4:1 multiplexer with a voltage controlled oscillator and clock multiplication unit, modulator drivers for electro-absorption and differential lithium-niobate modulators, trans-impedance amplifier, limiting amplifier and 1:4 demultiplexer with clock and data recovery circuit. The transceiver was used to teat optical transmission over a 2.26 km link with a 40 Gb/s, 231-1 pseudo-random bit sequence (PRBS) data. The transmitter achieves better than 12.9 dB extinction ratio, 1 ps added root mean square (RMS) jitter and 4 dBm output power. Without any optical amplification the receiver achieves -9.1 dBm back to back sensitivity at a bit error rate (BER) of 10-12 and a high dynamic range of 12.5 dBm.