Band‐pass distributed amplifiers

Abstract

A novel band‐pass distributed amplifier design concept is presented. The amplifier can be realized in monolithic form using GaAs FETs. The amplifier has excellent wideband gain and phase response characteristics. It shows promise for applications in the millimeter wave region. In this paper the results of analytical modelling as well as computer simulations are discussed.

Bandpass distributed amplifier design guidelines

“…The schematic of a bandpass distributed amplifier is shown in Figure l [2], which provide the appropriate midseries and midshunt image impedances at each section over a substantial portion of the passband.…”

“…The equation for the magnitude of the voltage gain is given by [2] where g , is the transconductance of the FETs, n is the number of FETs, R,, and R,, are the image impedances of the gate and drain lines at the band-center frequency, w,, X , ( = w/w,,) is the normalized frequency, 6 ( = w 2 -w,/w,) is the normalized bandwidth, w1 and w2 are the lower and the upper radian cut-off frequencies, and A , and Ad are the attenuations per section of the gate and drain lines, respectively. The equations for gate and drain line attenuations are given by [2] As in low-pass distributed amplifiers [l], here the gain at the band-center frequency cannot be increased without limit by adding FETs in the amplifier. The gain increases with the addition of FETs up to a maximum value, and any further addition of FETs beyond this number will only decrease the gain.…”

“…The ab product is a function of n, 6, and the device characteristic frequencies wd and wg. For a specified value of 6 (the same for gate and drain lines [2]) and a given device, one can plot ab-product curves on the ab plane with n as a parameter. These curves are a family of hyperbolas.…”

“…The design equations in [2] allow one to compute the values of the circuit elements of the gate and drain line sections of the amplifier [Figure l(a)].…”

“…They can be designed to operate beyond the cutoff frequency of the conventional low-pass distributed amplifiers [2]. These amplifiers have been analyzed [2] and demonstrated [3], but systematic design guidelines have not been presented in the literature. This article addresses the fundamental design considerations, and presents a graphical design approach that enables one to examine the trade-offs between the design variables to arrive at an appropriate design for a specified gain and bandwidth.…”