Guidelines for designing BJT amplifiers with low 1/f AM and PM noise

Abstract

In this paper we discuss guidelines for designing linear bipolar junction transistor amplifiers with low 1/f amplitude modulation (AM) and phase modulation (PM) noise. These guidelines are derived from a new theory that relates AM and PM noise to transconductance fluctuations, junction capacitance fluctuations, and circuit architecture. We analyze the noise equations of each process for a common emitter (CE) amplifier and use the results to suggest amplifier designs that minimize the 1/f noise while providing other required attributes such as high gain. Although we use a CE amplifier as an example, the procedure applies to other configurations as well. Experimental noise results for several amplifier configurations are presented.

One-port noise model of a crystal oscillator

“…Because we illustrated the theoretical results only by means of the example based on the crystal resonator measured by Curtis in [10] and studied in [2], and on the typical performance of a low-noise amplifier [9], we refrained from making generalizations. Nevertheless, several useful remarks can be made:…”

“…Furthermore, the results in [9] show that the amplitude psd exhibits on average a 4 to 5 dBc/Hz higher magnitude at f = 1 Hz and 2 to 4 dBc/Hz at 1 kHz. However, no claim is made that (31) and (32) are exhaustive.…”

“…Without mentioning the majority of possible feedback amplifier circuitries, we refer only to [9], where many measurements are reported. This assures us that the amplifier double-sided amplitude and phase psds may be modeled, at least in the first approximation, by:…”

Voltage adjustable attenuation with low 1/f noise

“…When the capacitance Cd is negligible, diodes can be used as voltagecontrolled variable resistors. The dc current through the diode exhibits l/f noise, a result of intrinsic noise in the diode [l] and power supply noise [2]. The dc current can thus be described by where A I 0 represent the lvnoise component and f is the frequency of the noise.…”

Flicker noise conversion in crystal oscillator

“…To simulate the amplifier noise, we refer to [7] and [8], where plenty of the experimental curves are reported. It makes sure that the amplifier residual amplitude noise spectral density may be modeled by…”