Curtis M. Grens

A Silicon-Germanium Receiver for X-Band Transmit/Receive Radar Modules

This work investigates the potential of commercially-available silicon-germanium (SiGe) BiCMOS technology for X-band transmit/receive (T/R) radar modules, focusing on the receiver section of the module. A 5-bit receiver operating from 8 to 10.7 GHz is presented, demonstrating a gain of 11 dB, and average noise figure of 4.1 dB, and an input-referred third-order intercept point (HP3) of -13 dBm, while only dissipating 33 mW of power. The receiver is capable of providing 32 distinct phase states from 0 to 360deg, with an rms phase error < 9deg and an rms gain error < 0.6 dB. This level of circuit performance and integration capability demonstrates the benefits of SiGe BiCMOS technology for emerging radar applications, making it an excellent candidate for integrated X-band phased-array radar transmit/receive modules.

Reliability of SiGe HBTs for Power Amplifiers—Part I: Large-Signal RF Performance and Operating Limits

This paper examines the performance and reliability implications associated with aggressively biased cascode SiGe HBT power-amplifier cores under large-signal RF operating conditions. The role of high-power RF stress on device degradation and failure is examined in detail. General expressions for a large-signal RF safe-operating area, which account for the effect of load impedance on the dynamic output current and voltage characteristics, are presented. These show excellent agreement with experimental results. Useful operating guidelines for reliable large-signal operation are provided.

An 850 mW X-Band SiGe power amplifier

An 850 mW SiGe power amplifier operating at X-Band (8.5-10.5 GHz) frequencies with over 11 dB of gain and 18% PAE is presented. This SiGe PA was implemented in a commercially-available, third-generation 130 nm 200 GHz SiGe BiCMOS platform using a hybrid high-breakdown / high-speed cascode pair to enhance voltage swing.

Reliability of SiGe HBTs for Power Amplifiers—Part II: Underlying Physics and Damage Modeling

This paper presents the underlying physics and modeling of aggressively biased cascode SiGe heterojunction bipolar transistor power amplifier (PA) cores under large-signal operating conditions. The damage characteristics observed during RF operation, particularly the base leakage and collector-base (CB) junction failure, are investigated in detail using dc stress methods. Base leakage was characterized across geometry, voltage, and current conditions, and a damage model is purposed based on Shockley-Read-Hall theory and the reaction-diffusion equation. This model is used to predict damage under aggressive RF operations, in order to extract the operational lifetime of SiGe PAs. The onset of CB junction failure was modeled using the current-gain collapse model, and it accurately captures the failure threshold current I Fail observed during RF stress.

Compact Modeling of Mutual Thermal Coupling for the Optimal Design of SiGe HBT Power Amplifiers

Most bipolar-transistor compact models incorporate some level of self-heating capability in order to determine the impact of thermal effects on circuit performance. Techniques for predicting mutual-thermal-coupling effects, however, are not readily available within most commercial CAD platforms. Presented in this brief is a technique which allows for the easy modification of design-kit-supplied models to predict and optimize mutual thermal coupling using commonly available CAD tools such as Cadence and Spectre.

The Effects of Scaling and Bias Configuration on Operating-Voltage Constraints in SiGe HBTs for Mixed-Signal Circuits

This paper presents a comprehensive picture of operating-voltage constraints in SiGe heterojunction bipolar transistors, addressing breakdown-related issues as they relate to technology generation, bias configuration, and operating-current density. New definitions for breakdown voltage, adopted from standard measurements, are presented. Practical design implications and physical origins of breakdown are explored using calibrated 2-D simulations and quasi-3-D compact models. Device-level analysis of ac instabilities and power performance, which is relevant to mixed-signal circuit design, is presented, and implications of the relaxed voltage constraints for common-base operation are explored.

On Common–Base Avalanche Instabilities in SiGe HBTs

This paper presents a detailed investigation of the key device-level factors that contribute to the bias-dependent features observed in common-base (CB) dc instability characteristics of advanced SiGe HBTs. Parameters that are relevant to CB avalanche instabilities are identified, extracted from measured data, and carefully analyzed to yield improved physical insight, a straightforward estimation methodology, and a practical approach to quantify and compare CB avalanche instabilities. The results presented support our simple theory and show that CB-instability characteristics are strongly correlated with the parasitic base and emitter resistances. The influence of weak quasi-pinch-in effects are shown to contribute additional complexity to the bias dependence of the CB-instability threshold. Measured data from several technology nodes, including next-generation (300-GHz) SiGe HBTs, are presented and compared. Experimental analysis comparing different device geometries and layouts shows that while device size plays an important role in CB avalanche instabilities across bias, these parameters are not sensitive to standard transistor layout variations. However, novel measurements on emitter-ring tetrode transistor structures demonstrate the influence of perimeter-to-area ratio on CB stability and highlight opportunities for novel transistor layouts to increase .

Assessing reliability issues in cryogenically-operated SiGe HBTs

We assess SiGe HBTs for emerging mixed-signal cryogenic circuits designed to operate on the Moon without ambient heating or cooling (from +120C to as low as -230C), focusing of potential reliability issues. Comprehensive mixed-mode reliability stress data for these SiGe HBTs were measured from 300 K to 85 K. We extract the thermal resistance over temperature to evaluate the impact of the self-heating at low temperatures, explore the low-frequency noise performance at room temperature and cryogenic temperatures as a function of stress condition, and examine the impact of cooling on breakdown voltage and operating point instabilities for mixed-signal circuits.

A Monolithic 5-Bit SiGe BiCMOS Receiver for X-Band Phased-Array Radar Systems

This work presents a 5-bit receiver for X-band phased-array radar applications based on a commercially-available silicon-germanium (SiGe) BiCMOS technology. The receiver achieves a gain of 11 dB, an operational bandwidth from 8.0 to 10.7 GHz, an average noise figure of 4.1 dB, and an input-referred third-order intercept point (IIP3) of-13 dBm, while only dissipating 33 mW of power. The receiver also provides 32 distinct phase states from 0 to 360deg, with an rms phase error < 9deg. This level of circuit performance and integration capability demonstrates the benefits of SiGe BiCMOS technology for emerging radar applications, making it an excellent candidate for integrated X-band phased-array radar transmit/receive modules.

Modeling mixed-mode DC and RF stress in SiGe HBT power amplifiers

The degradation of SiGe HBTs due to mixed-mode DC and RF stress (simultaneous application of high current and voltage) has been modeled for the first time. State-of-the-art 200 GHz SiGe HBTs were first characterized, and then DC and RF stressed. Using TCAD simulations and calculations based upon a reaction-diffusion model, the excess base current due to stress was modeled as a function of the stress current and voltage. This physics-based stress model was then designed as a sub-circuit in Cadence, and incorporated into a cascode SiGe PA design to predict the DC and RF stress-induced excess base current. Predicted degradation is in agreement with RF stress results.