Single OTRA Based Analog Multiplier and Its Applications

This paper presents an analog multiplier using single operational transresistance amplifier (OTRA). The proposed circuit is suitable for integration as it does not use any external passive component. It can be used as a four-quadrant multiplier. Theoretical propositions are verified through PSPICE simulations using 0.5？μm CMOS parameters provided by MOSIS (AGILENT). The simulation results are in close agreement with theoretical predictions. The workability of the proposed multiplier is also tested through two applications, namely, a squarer and an amplitude modulator. 1. Introduction Analog multipliers find extensive application in the field of telecommunication, control, instrumentation, measurement, and signal processing [1]. A number of circuits are reported in literature relating to analog multipliers [1–12]. Circuits presented in [2–7] are based on Gilbert multiplier [12] and are suitable for CMOS integrated technology. The other class of the circuits is implemented using active analog blocks such as operational transconductance amplifier [1], differential difference current conveyors [8], current feedback amplifiers [9], current-controlled current conveyor [10], and current difference buffered amplifier [11]. Recently the OTRA has emerged as an alternate analog building block [13–26] which inherits all the advantages of current mode techniques. The OTRA is a high gain current input voltage output device. The input terminals of OTRA are internally grounded, thereby eliminating response limitations due to parasitic capacitances and resistances [13] at the input. Several high performance CMOS OTRA topologies have been proposed in the literature [13–16]. In the recent past OTRA has been extensively used as an analog building block for realizing a number of analog signal processing [17–21] and generation circuits [22–24]. This paper presents a single OTRA based low voltage analog multiplier which does not use any external passive components and hence is suitable for integration. The proposed circuit can be used as a four quadrant multiplier without any change of topology. The workability of the proposed multiplier is demonstrated through two applications, namely, a squarer and an amplitude modulator. 2. The Proposed Multiplier Circuit 2.1. OTRA OTRA is a three-terminal device, shown symbolically in Figure 1 and its port relations are characterized by the following matrix: where is transresistance gain of OTRA. For ideal operations approaches infinity and forces the input currents to be equal. Thus OTRA must be used in a negative feedback configuration.