Wireless Integrated System Laboratory

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Research

Substrate-shielded transmission-line used in the amplifier

The Figures show cross-sectional view of substrate-shielded transmission-line used in the amplifier. Six metal layers are available in 0.18-μm CMOS technology. The top metal-6 layer is 2.0 μm thick and the distance from metal-1 layer is about 7 μm. The metal-1 layer effectively prevents electric field penetrating in the conductive silicon substrate. All the metal layers were slotted for metal stress relief. Below metal-1, polysilicon layer covers the slots, and the metal-1 and polysilicon was connected by vias. The metal-1 and silicon substrate was connected by multitude of vias to reduce substrate resistance and ground inductance.

 

Recently, there is growing interest for short-range, high data rate wireless system based on low cost microwave integrated circuits (MMICs). In the past, MMICs based on III-V semiconductor technologies have been preferred for these applications due to their higher electron mobility, higher breakdown voltage, and availability of high-Q passives. To satisfy the new need for broadband wireless system in the commercial market, however, CMOS technology is the most viable option due to its potential for low cost and mass production capabilities.

Ka-band 3-stage CMOS power amplifier

A Ka-band 3-stage CMOS power amplifier was designed and fabricated using 0.18-μm gate-length common-source transistors. For low loss and accurate matching networks for the amplifier, a substrate-shielded microstrip-line was used with good modeling accuracy up to 40 GHz.

 

A Ka-band 3-stage power amplifier was developed in 0.18 μm CMOS technology using new substrate-shielded coplanar waveguide (CPW). The new CPW structure reduces the loss from conductive silicon substrate allowing high gain for the amplifier. Broadband model of substrate-shielded CPW in conjunction RF transistor model up to 40 GHz resulted in accurate gain matching of the amplifier.

 

we investigated a new substrate-shield CPW for low loss matching element for a Ka-band power amplifier using 0.18 μm CMOS technology. The measured and modeled S-parameters of transistors and substrate-shield CPW showed good agreement allowing accurate gain matching at 26.5 GHz. The fabricated 3-stage amplifier achieved a 12 dB small-signal gain and a 12.5 dBm output power at 26.5 GHz, which agreed well with the modeled results.

 

Because the transistor model provided by foundry has limited accuracy at millimeter-wave frequency, additional parasitic elements were added to the foundry BSIM3 model using measured S-parameters. The measured maximum power gain (fmax) and current gain (fT) for NMOS device (W/L=20 ?2 μm/0.18 μm) was 54 GHz and 85 GHz when biased at  IDS = 13 mA (0.33 mA/ μm) and VDS = 1.8 V. The measured data were smooth and agreed well with the simulated ones.

 K-band CMOS amplifier

This figure presents high efficiency and high power CMOS amplifiers operating at K-band frequencies. The amplifiers employed the series-bias technique to increase the operating voltage and achieved a high output power level. The technique also allowed the power amplifiers to operate at a low DC current and thus high efficiency was obtained.

 Q-band CMOS power amplifier

A high efficiency Q-band CMOS power amplifier was fabricated using a 0.13 μm standard CMOS process with six layers of copper metallization. To achieve high efficiency, a tapered device sizing technique was employed with a common-source transistor rather than a cascode configuration. Using tapered device sizing, DC power consumption was reduced by using small size transistors in the driver stage while maintaining the overall amplifier gain and output power.  

 

Standard 0.13 μm CMOS backend provided a thin copper top metal. The loss of a transmission line 6 μm wide was -1.1 dB/mm at 25 GHz for thin copper metal (0.9 μm), while the loss was -0.65 dB/mm using a thick (3 um) copper metallization option. The result shows that thick metal in general has low loss, but it is possible to use a standard digital process for cost reduction.

3-stage Q-band power amplifier

This figure shows the circuit of a 3-stage Q-band power amplifier. The unit finger width was 2 μm, and the size of the transistors was tapered to increase the amplifier efficiency while providing reasonable output power. In general, SiGe HBT technology can provide higher power gain than CMOS technology at millimeter-wave frequencies. Also, there are relatively large losses in the matching network implemented using transmission lines and inductors fabricated using a standard CMOS backend.

 Voltage controlled oscillator (VCO)

we present a novel low power voltage-controlled-oscillator (VCO) structure based on bandwidth enhancement technique. The VCO was fabricated in 0.13 μm standard CMOS process having 6 layers of copper metallization. Due to broadband nature of the enhanced oscillator structure, the VCO operates at a low supply voltage of 0.5 V while consuming 1 mW power. The oscillation frequency ranges from 4.48 to 4.82 GHz with a turning range of 7.5 %.

Vackar VCO

we present measured performance of differential Vackar voltage-controlled oscillator (VCO) implemented for the first time in CMOS technology. The Vackar VCO provides good isolation between the LC tank and loss-compensating active circuit, thus, excellent frequency stability is achieved over frequency tuning range. The Vackar VCO was implemented using nMOS transistors and LC tank in 0.18 μm RF CMOS process.

Clapp VCO

An excellent phase noise differential Clapp VCO fabricated in CMOS technology is presented in this papers. The VCO operates at the frequency of 4.6GHz and consumes a power of 4.2mW with 1.0 V voltage supply, the VCO show a very good phase noise is about -119dBc/Hz at 1MHz offset. Comparative analysis was performed on the gm (start-up) and oscillation amplitude condition including transistor parasitic for common-drain and common-gate.

 

we present measured performance of differential Vackar voltage-controlled oscillator (VCO) implemented for the first time in CMOS technology. The Vackar VCO provides good isolation between the LC tank and loss-compensating active circuit, thus, excellent frequency stability is achieved over frequency tuning range.

Tuned-in tuned-out (TITO) oscillator

A new voltage-controlled-oscillator (VCO) based on tuned-in tuned-out (TITO) oscillator is presented. Because of better flicker noise, PMOS TITO VCO achieves an excellent performance. By adjusting two control bias voltages, a wide range output frequency was obtained. Consuming a power of 2.7mW with 0.9 V voltage supply, the VCO shows a good output frequency turning range of 6.5% from 4.6 to 4.8GHz. Phase noise is about -114 dBc/Hz at 1MHz offset.

Millimeter-wave wireless transceiver

Millimeter-wave wireless transceiver building blocks were fabricated using Dongbu Hitek 0.13μm RFCMOS technology. The building blocks include a broad-band low noise amplifier operating over 40-50 GHz with more than 18 dB gain, a 40 GHz tuned power amplifier delivering more than 14 dBm output power, and a voltage-controlled oscillator operating at 18 GHz. Good agreement between the measured and modeled data were obtained for these circuits. These results is believed to be the first demonstration of measurement and modeling validation of millimeter-wave circuits using Dongbu Hitek 0.13um RFCMOS RF CMOS technology.

 

Both in research and commercial area, there are growing interest in the millimeter-wave integrated circuits and systems for short-range and high data rate radio communication. Also, the frequency allocation of 57-64 GHz for unlicensed usage paved a way for Gbps date rate uncompressed wireless transmission. Low cost is necessary to fully benefit from high quality information service using high speed data communication. Therefore, integrated system rather than module-based assembly is required to facilitate mass production required for wide spread commercial adoption of millimeter-circuit technology. Due to the low cost, recent rapid gate-length scaling, and great potential for mm-wave systems-on-chip, there is high demand for low-cost CMOS building blocks at millimeter-wave frequency bands

 

 

 

For low noise figure, the first stage was designed using common-source transistor while the 2nd and 3rd stages employed cascode configuration for high gain. Spiral inductors were used for on-chip biasing and the chip size was compact with 0.65 ?1.0 mm2 including test pad. While foundry device model for common-source transistor is usually accurate, there may be uncertainty for common-gate transistor configuration. The length between the common-source and common-gate transistors was optimized for high gain. Substrate-shielded transmission line was used for its inherent modeling accuracy compared to lumped inductor. Shunt matching elements were implemented using lumped capacitors.

 

High Power Performance 60 GHz Push-Push Oscillator MMIC in Metamorphic HEMT Technology

 

Heterostructures of InAlAs/InGaAs metamorphic high-electron mobility transistor (mHEMT) have attracted widespread attention for their high power and high frequency capability with low cost compared to lattice matched HEMTs on InP substrates. By using the optimized indium content in the channel, the advantages of high breakdown characteristics of GaAs pHEMT and the excellent millimeter-wave performance of InP HEMT can be combined. A high power 60 GHz push-push oscillator was fabricated using 0.1 μm GaAs metamorphic high electron-mobility transistors (mHEMTs). The devices with a 0.12 Ám gate-length exhibited good DC and RF characteristics such as a maximum drain current of 700 mA/mm, a peak gm of 660 mS/mm, and an fT of 170 GHz. 

 

By combining two sub-oscillators having 6 ?50 μm periphery mHEMT, the push-push oscillator achieved 5.8 dBm of output power at 59.9 GHz with good fundamental suppression. The phase noise of -81.5 dBc/Hz at 1 MHz offset was measured. This is the first monolithic push-push oscillator at 60 GHz fabricated using mHEMT technology, and demonstrates a potential of mHEMT for cost effective millimeter wave commercial applications.

 

The left figure shows the V-band microwave test setup used to measure the oscillator performance. For on-wafer measurement of both output power and oscillation frequency, the output of push-push oscillator is connected to a RF probe, and then to a WR-15 V-band waveguide. The output spectrum and phase noise performance at 60 GHz were measured using Agilent E4448A spectrum analyzer. The oscillation frequency is determined by down-converting the signal by an Agilent 11970V harmonic mixer via a 10 dB WR-15 coupler. The output power at 60 GHz was measured using a V8486A power sensor (50~75 GHz) and HP 438A power meter.

 

The left figure shows the measured output spectrum of the push-push oscillator. The oscillation frequency of 59.5 GHz with 6.3 dBm of output power was measured at VDS = 1.9 V and VGS = –0.46 V. The oscillator output power and tuning frequency characteristic depending on VGS is shown in Fig. 6. The loss of probe tip, waveguide components, and coupler in the V-band measurement setup is about 3.5 dB, and is accounted for correcting the measured output power. Over VGS = –0.43 to –0.48 V, the output power ranged from 6.8 dBm to 5.8 dBm with the oscillation frequency changed from 58.7 to 59.9 GHz. This corresponds to a tuning range of 2.0 %. To examine the correct push-push oscillation and fundamental suppression, the fundamental oscillation frequency at f0 was measured using conventional 2.4 mm coaxial cable measurement setup. The fundamental power suppression of more than 35 dBc.

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