Fazal Ali

Direct conversion radio for digital mobile phones-design issues, status, and trends

Applications of direct frequency-conversion techniques have been rapidly getting attention of radio designers worldwide. This paper focuses on bringing out key implementation challenges of direct conversion receivers and transmitters targeted for different second- and third-generation mobile phone standards like global system for mobile communication, code division multiple access (cdmaOne and CDMA 2000), and wide-band code division multiple access. Techniques and tradeoffs to arrive at optimal implementation are highlighted. Some of the commercially available application-specific integrated circuits that are based on direct conversion architecture and their salient features are summarized.

A wide-band GaAs monolithic spiral quadrature hybrid and its circuit applications

The design, performance, and circuit applications of a 2-6-GHz GaAs monolithic spiral quadrature coupler are presented. This 90 degrees coupler uses lumped spiral inductors and metal-insulator-metal (MIM) capacitors and is very small in size (14 mil*26 mil). The measured relative phase difference between the coupled and direct port over the 3:1 bandwidth was 93 degrees +or-6 degrees . Applications of this broadband hybrid in reflection phase-shifter, image-reject downconverter, and I-Q downconverter circuits have also been successfully demonstrated based on this structure. >

A 1.8-W, 6-18-GHz HBT MMIC power amplifier with 10-dB gain and 37% peak power-added efficiency

A two-stage 6-18-GHz high-efficiency AlGaAs-GaAs HBT MMIC power amplifier has been designed and tested. At 7-V collector bias, this fully matched monolithic amplifier delivered an output power of 1.8+or-0.6 W over the band. The peak output power was 2.45 W at 13 GHz with an associated gain of 11.1 dB and 36.7% power-added efficiency (PAE). Amplifiers from five different wafers showed similar performance.<<ETX>>

Broadband, low-loss 5- and 6-bit digital attenuators

Low-loss 5- and 6-bit MMIC digital attenuators covering DC-16 GHz have been designed, fabricated and tested. These attenuators provide exceptional performance, with reference state insertion loss of less than 5 dB at 16 GHz (for the 6-bit chip) and 28 dB of dynamic range of attenuation. The input and output VSWRs of the attenuators are better than 1.6:1 over all attenuation states and frequencies. These digital attenuators have an input third order intercept point of 37 dBm.<<ETX>>

A 2 watt, 8-14 GHz HBT power MMIC with 20 dB gain and >40% power-added efficiency

A two-stage, 8-14 GHz high-efficiency AlGaAs/GaAs HBT MMIC power amplifier has been designed and tested. At 7 V collector bias, this common-emitter monolithic amplifier has achieved 20 dB gain, 33 dBm (CW) output power, and >40% power-added efficiency over the 8-14 GHz band. The amplifier is designed for 25 /spl Omega/ input and output impedance, and all the matching networks, as well as biasing circuits, are contained within this HBT MMIC. To our knowledge, this is the highest efficiency, the highest gain, and the highest output power reported for any monolithic power amplifier covering a 6 GHz bandwidth in the X-Ku band. >

A novel cascode feedback GaAs MMIC LNA with transformer-coupled output using multiple fabrication processes

The design, development, and performance of a novel high dynamic range cascode feedback GaAs MMIC LNA with transformer-coupled output is presented. The baseline design (chip size: 48*48 mils) operates over any 1-GHz bandwidth (with a simple off-chip input inductor) in the 0.5-3-GHz frequency range and has typically 15-dB small signal gain, 2.1-dB noise figure, and greater than 15 dBm of output power at 1-dB gain compression point. Performance results of this circuit fabricated in three different foundry processes are presented.<<ETX>>

A 1-watt X-Ku band HBT MMIC amplifier with 50% peak power-added efficiency

A broadband, high-efficiency MMIC power amplifier has been developed using AlGaAs-GaAs heterojunction bipolar transistors (HBTs). At 7-V collector bias, the fully matched monolithic amplifier produced 31-dBm CW peak output power with 9.2-dB peak gain and 50% peak power-added efficiency in the 8-15-GHz band. Several amplifiers from five different wafers have ben successfully tested.<<ETX>>

A 5-10 GHz, 1-Watt HBT amplifier with 58% peak power-added efficiency

Four 0.25-W GaAs Heterojunction Bipolar Transistors (HBTs) were combined in a single-stage hybrid microstrip amplifier. An output power of minimum 1 Watt (W) was achieved over the 5.5-9.5 GHz band with >48% power-added efficiency (PAE). The peak PAE was 58% at 7 and 9.5 GHz with an average efficiency of 52% over the 5-10 GHz band. This result was reproduced on two more units with a minimum efficiency of 48% and an average efficiency of 51%. To our knowledge, this is the highest efficiency obtained from any 1-W amplifier covering 5-10 GHz bandwidth. >

A 1-Watt, 8-14-GHz HBT amplifier with >45% peak power-added efficiency

Four 0.25-W gallium arsenide heterojunction bipolar transistors (HBTs) were combined in a single-stage hybrid microstrip amplifier. An output power of >1 W was achieved over the 8.5-13.5-GHz band with >35% power-added efficiency (PAE). The peak PAE was 45.4% at 12.5 GHz. This result was repeated on a second unit that was subsequently tuned for improved performance at the upper end of the band. The PAE at 14 GHz increased to >43% with 1-W output while, at 8 GHz, it remained at approximately 30%.<<ETX>>

A study of Class C operation of GaAs power HBTs

GaAs power HBTs are traditionally biased in Class A or Class AB mode for power amplifiers. This paper describes the tradeoffs of operating these devices in Class C bias. We find that power-added efficiency (PAE) improves and power gain decreases in Class C when compared to Class AB bias. At 6 GHz, the PAE increased by greater than 10 percentage points (from 68.9% in Class AB to 80.6% in Class C) with concurrent loss of 4.3 dB in power gain. The efficiency improves monotonically with lower operating frequency. In a single-tone environment, the second harmonic increases by /spl sim/7 dB in Class C over Class AB. To our knowledge, this is the first report on the experimental study of Class C operation of GaAs HBTs.<<ETX>>