A simple approach for the implementation of CMOS amplifiers with constant bandwidth independent of gain

Abstract

In this paper we discuss an efficient implementation of the Cherry-Hooper amplifier scheme based on a new OTA structure. This is used to design highly linear CMOS amplifiers with programmable and accurate gain and high bandwidth that remains approximately constant with gain adjustment. A fully differential VGA with 30MHz approximate constant bandwidth and accurate digitally adjustable gain from 1 to 128 in 0.5µm CMOS technology is discussed. Experimental verification of the proposed scheme is also provided.

A practical near constant bandwidth amplifier

“…Equation (10) also illustrates the well known non-linear relation between and f −3dB . For 1 and G it can be shown after some difficulty that (10) reduces to (2), which is to be expected. To illustrate this non-linear relationship a plot of the normalized −3dB versus to four gains G = 1, 5, 10, 25 for a given is shown in Figure 3.…”

“…In recent years the need for high-speed amplifiers with large bandwidths has fuelled the rapid growth and development of current feedback amplifiers (CFAs) [1]. A great deal of research has led to commercial amplifiers with bandwidths in the order of a few GHz and slew rates in excess of 1000 V/ s with in-house amplifiers having less bandwidths and smaller slew rates [2][3][4]. A major feature of these amplifiers is their near constant bandwidth with varying gain arising from the voltage-shunt feedback employed in the circuit.…”

Adaptive frequency compensation for maximum and constant bandwidth feedback amplifiers

“…The gain-bandwidth conflict is one of the main limitations experienced by conventional operational amplifiers and is the fundamental obstacle to achieve wide bandwidths as well as large gains. Several attempts have been reported to avoid this drawback [1][2][3][4][5][6][7][8][9][10][11]. However, all the known solutions do not improve the basic operational amplifier topology; instead, they find alternative amplifier architectures.…”

Constant bandwidth gain-linear programmable gain amplifier

“…There are several other approaches to improve the bandwidth performance of PGAs such as adaptive frequency compensation technique [5] and OTA-op-amp amplifier technique [6]. For adaptive frequency The structure shown in figure 2 is improved on the basis of structure shown in figure I, The transistors P I and P2 as the differential load are connected in a diode mode, the tail current source 11 is in parallel with current source 12, 13, 14.The output impedance of the proposed amplifier is:…”