Influence of collector design on InGaP/GaAs HBT linearity

Abstract

Linearity characteristics of InGaPlGaAs heterojunction bipolar transistors with various collector profiles are examined. Output third-order intercept point is measured as a function of bias current and voltage a t 5GHz. The results from this study indicate that IP3 varies with current in a complex manner and is significantly dependent on the collector design. A dynamic trend in IP3 is observed where a peak occurs at a current just below Kirk effect and a trough occurs at the onset of Kirk effect. Although the Gummel-Poon model is not able to predict this behavior, a large signal HBT model, which accounts for collector space-charge effects such as electron velocity modulation and Kirk effect, can properly represent the measured data. For accurate Linearity predictions, these effects should be incIuded in a large signal HBT model.

A theory of high-frequency distortion in bipolar transistors

“…As detailed in Appendix IV, the limit embodies a cancellation of third-order intermodulation currents generated by the transistor's nonlinear transconductance and nonlinear stored charge; furthermore, can be expressed in terms of the series coefficients in (18) and (19), and in terms of the lower order mixing voltages appearing across the transistor's base-emitter terminals, as follows:…”

“…To examine this phenomenon more closely, it is necessary to write (16) in an alternative form. In terms of the power-series coefficients used in [10], namely, those in the expansions (18) and (19) where is the low-frequency common-base current gain, (16) can be written as follows: (20) Of interest in (20) is the term (21) in the numerator of the last factor. As pointed out in [10], this term embodies a subtraction, or cancellation, of second-order current components arising from the device's nonlinear transconductance and nonlinear stored charge; these currents are proportional to and , respectively.…”

“…More recently, Maas et al [10] attributed the surprisingly good linearity of heterojunction bipolar transistors (HBTs) working at high frequencies to a cancellation of nonlinear currents arising from the dynamic resistance and capacitance of the emitter-base junction. This analysis was followed by a number of studies that were mostly of an empirical nature, leading to various observations on the factors affecting high-frequency distortion; for example, comments were made on the role of current cancellation [11]- [14], the feedback effect of the parasitic base and emitter resistances [15], [16], the impact of the nonlinear, collector-base depletion capacitance [14]- [19], the importance of base-collector transit time [16], [19], and the choice of bias voltage and current [14], [16]- [20]. Studies have also been undertaken to examine the distortion behavior of other important microwave devices; for example, Pedro et al [21]- [23] recently examined distortion in metal-semiconductor field-effect transistors (MESFETs).…”

A Genetic Algorithm Approach to InGaP/GaAs HBT Parameter Extraction and RF Characterization

“…[1][2][3][4][5][6] One of the most favorable properties of HBT devices is the unusually high linearity at relatively low levels of DC power. Various approaches have been proposed to calculate the intermodulation distortion and two-tone characteristics for a HBT device in both time and frequency domains.…”

“…Various approaches have been proposed to calculate the intermodulation distortion and two-tone characteristics for a HBT device in both time and frequency domains. [1][2][3][4][5][6][7][8][9][10] However, the extraction and optimization of the equivalent circuit model, as well as its parameters, for both DC characteristics and RF property of the HBTs are typically accomplished in either of two fundamental approaches: numerical optimization or direct parameter extraction. [5][6][7][8] These approaches have their merits, but they may have local optimization, divergence, and time-consuming problems.…”