A practical near constant bandwidth amplifier

Abstract

SUMMARYThis paper presents a simple near constant bandwidth amplifier constructed from two operational amplifiers. The near constant bandwidth is obtained by reducing the normally high input impedance of the opamp via local and overall feedback. Experimental results obtained using identical opamps and different opamps verify the expected theoretical results.

Versatile composite amplifier configuration

“…As previously indicated, the CCA aggregates the high DC stability of the OPA and the high speed of the CFA while the PCA brings together the constant bandwidth of the CFA and the high voltage and high current output of the OPA. The constant bandwidth characteristic is demonstrated in the graphs of Figures 7 and 8, and it is instructive to compare this property in the CCA, the PCA and the two-OPA composite amplifier published in Maundy et al (2009), which uses OPAs in the same configuration as the PCA. These along with a single CFA and an enhanced CFA (Gift & Maundy, 2005) are summarised in Table 1, where constant bandwidth is indicated by the absence of R 1 in the bandwidth expression.…”

“…The two-OPA composite amplifier discussed in Maundy et al (2009) that introduced the configuration used in the PCA employs feedback around the input OPA of the configuration applied to the highimpedance inverting terminal in order to create a low-impedance terminal that realises the near constant bandwidth.…”

“…Here, the input device is the CFA and the output device is the desired OPA. It is exactly the same configuration used in Maundy et al (2009) but here a CFA is used instead of an OPA as the input device. The inverting inputs of both devices are connected while the output of the CFA is connected to the non-inverting input of the OPA.…”

“…The proposed CFA-OPA composite amplifier employs the same configuration used in the OPA-OPA configuration in Maundy et al (2009), with the introduction of the CFA in place of the input OPA. The equivalent circuit of the CFA that would be used in the analysis is shown in Figure 1, where r x is the input resistance at the inverting input of the CFA and R z is its low-frequency transresistance.…”

“…These modules usually involve the operational amplifier (OPA), and they have been used to increase loop gain (Franco, 2002), phase accuracy (Graeme, 1993;Wong, 1987), bandwidth (Geiger, 1977;Stofka, 2008), noise reduction (Schmid, 1994) and bandwidth constancy (Maundy, Gift, & Westwick, 2009) in amplifier systems. They have also been applied in active filters (Budak, Wullink, & Geiger, 1980;Geiger & Budak, 1979) and oscillators (Wojtyna, 1992).…”