Symbolic analysis and design of current-differencing-amplifier filters

1) Institut GOŠA d.o.o., Milana Rakića 35, 11000 Belgrade, SERBIA 2) Faculty of Electrical Engineering, Bul. kralja Aleksandra 73, 11120 Belgrade, SERBIA Introduction ANY industrial electronic control systems are designed to operate using only a single-power-supply voltage. The conventional integrated-circuit operational amplifier (IC op amp) is typically designed for split power supplies (±15 V DC) and suffers from a poor output voltage swing and a rather large minimum common-mode input voltage range (approximately +2 V DC) when used in a single power supply applications. In addition, some of performance characteristics of these op amps could be sacrificed – especially in favor of reduced costs. To meet the needs of the designers of low-cost, singlepower-supply control systems, a new internally compensated amplifier has been designed that operates over a power supply range of +4 V DC to 36 V DC with small changes in performance characteristics and provides an output peak-to-peak swing that is only 1 V less than the magnitude of the power supply voltage [1]. The new amplifier, Fig.1, is designated Current-Differencing Amplifier (CDA), and represents a departure from a conventional amplifier design. Instead of using a standard transistor differential amplifier at the input, the noninverting input function has been achieved by making use of a “current-mirror” to “mirror” the non-inverting input current about ground and then to extract this current from that which is entering the inverting input terminal. Whereas the conventional operation amplifier (OPAMP) differentiates input voltage, this amplifier differentiates input currents and therefore the name “Norton Amp” has been used to indicate this new type of operation [1,2]. It is also well known that the frequency range of active filters using operation amplifiers is limited due to the finite OPAMP’s bandwidth. Since the CDA as a current processing device has a much wider bandwidth than the classical OPAMP [3], its use in active filter realizations can significantly improve the useful filter bandwidth. Figure 2. Current-Differencing Amplifier symbol