AN644 Datasheet, PDF (1/6 Pages) Maxim Integrated Products – QuickChip Design Example 2 Low Power Silicon BJT LNA for 1.9GHz

ASICs
Application Note 644: Mar 17, 2000
QuickChip Design Example 2
Low Power Silicon BJT LNA for 1.9GHz
1998 IEEE. Reprinted, with permission, from 1998 IEEE Microwave and Guided Wave Letters, Vol. 3, No. 3, pp. 136-137
Abstract
A two-stage 1.9GHz monolithic low-noise amplifier (LNA) with a measured noise figure of
2.3dB and an associated gain of 15dB was fabricated in a standard silicon bipolar transistor
array. It dissipates 5.2mW from a 3V supply including the bias circuitry. Input return loss and
isolation are -9dB and -20dB, respectively.
I. Introduction
In portable communication equipment, such as cellular phones and digital cordless phones,
manufacturers are trying to replace as many discrete devices as possible with high-density ICs
to be competitive in size, weight, power dissipation, and price. In a number of recent papers
low power LNAs for S-band have been described [1,2,3]. These LNAs were fabricated using
some sophisticated GaAs full-custom processes. Since the high frequency performance of state-
of-the-art silicon bipolar processes are continuously improving lowcost semi-custom arrays
with a limited choice of components provide a reasonable solution for RF applications.
In order to demonstrate such a solution, we present in this letter a very low-power monolithic
1.9GHz silicon LNA which draws a total current of 1.75mA including bias circuit.
II. Circuit Design
A schematic of the two-stage LNA is shown in Fig. 1. The circuit employs a high-gain
common-emitter stage (Q1-RL) and a emitter-follower output stage (Q2-Q3). This approach
eliminates the need for coupling capacitors. The current of the first stage is set by a resistive
parallel feedback (R3 and R4), which is connected to the external matching inductor (L1) such
that no noise degradation occurs. Thus, only a single supply voltage is required. This feedback
also improves both the bias and RF stability of the amplifier.
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