428 J. KOTON, A. LAHIRI, N. HERENCSAR, K. VRBA, CURRENT-MODE DUAL-PHASE PRECISION FULL-WAVE RECTIFIER... Current-Mode Dual-Phase Precision Full-Wave Rectifier Using Current-Mode Two-Cell Winner-Takes-All (WTA) Circuit Jaroslav KOTON 1 , Abhirup LAHIRI 2 , Norbert HERENCSAR 1 , Kamil VRBA 1 1 Dept. of Telecommunications, Brno University of Technology, Purkynova 118, 612 00 Brno, Czech Republic 2 36B J and K Pocket, Dilshad Garden, Delhi-110095, India koton@feec.vutbr.cz, lahiriabhirup@yahoo.com, herencsn@feec.vutbr.cz, vrbak@feec.vutbr.cz Abstract. In addition to the recently proposed full-wave rectifier by Prommee et al. [25] using voltage-mode (VM) two-cell winner-takes-all (WTA) circuit, we present current- mode (CM) precision full-wave rectifier using CM two-cell WTA circuit. The popular Lazzaro’s CM WTA circuit has been employed for the purpose and there is no requirement of inverting the input signal as in [25]. Also, dual compli- mentary phases of the output current signal are available from high-output impedance terminals for explicit utiliza- tion. As compared to many recently proposed CM rectifiers using complex active devices, e.g. dual-X current conveyor or universal voltage conveyor, our circuit is very compact and requires a total of 21 transistors. SPICE simulation re- sults of the circuit implemented using 0.35 μm TSMC CMOS technology are provided which verify the workability of the proposed circuit. Keywords Analog signal processing, current-mode, precision full- wave rectifier, instrumentation, measurement, WTA circuit. 1. Introduction Precision rectifiers serve as very important blocks for instrumentation and measurement and they are used in nu- merous applications such as ac volt- and ampere-meters, signal polarity detectors, frequency doubling, RMS to DC conversion, peak/valley detection and averaging circuit [1]. Consequently, a number of realizations of both voltage- mode (VM) and current-mode (CM) precision rectifiers us- ing variety of active building blocks (ABBs) can be found. Basic and well known solutions using operational ampli- fiers [1] operate well only at low frequencies [2], [3] due to the finite slew-rate and effects caused by diode com- mutation. Therefore, for high-frequency applications other active elements such as current conveyors (CCs) [4]–[8], current-controlled current differencing buffered amplifiers (CC-CDBAs) [9], operational transconductance amplifiers (OTAs) [10]–[12], current differencing transconductance amplifiers (CDTAs) [13], [14], voltage conveyors (VCs) [15] (and references cited therein). Most of these realizations are non-optimal in terms of the number of transistors em- ployed and they require multiple ABBs (often, with unused terminals) for their creation. For example, the CM recti- fier in [9] employs three CC-CDBAs. The resulting circuit has several unused terminals of the employed ABBs, e.g. the w terminals of the second and third CC-CDBA are un- used, that is, the voltage-buffers of the second and third CC- CDBA have no functionality and should be removed, since they unnecessarily consume the biasing current and serve no “real-purpose”. Similarly, the circuits in [15], employ- ing current and voltage conveyor, also have several unused terminals which are not required. An interesting all-CMOS rectifier has been proposed in [16] which utilized the class B operation of the CMOS second-generation current con- veyor (CCII). This circuit, however, requires the input cur- rent signal to be four times more than the biasing current of the CCII, i.e. I in > 4I B and thus offers reduced preci- sion for very low input signal amplitudes. The circuit also requires differential current signals for full-wave rectifica- tion. Other solutions of all-CMOS precision rectifiers can be found in [17]–[19]. In [18] and [19] the authors present a high-frequency half-wave rectifier that, however, requires a number of different bias currents and is generally based on the solution of an full-wave rectifier already discussed in [20], where current conveyor and current mirrors are used. One of the most recent additions to all-CMOS preci- sion rectifiers is by Minaei et al. [21]. The circuit in [21] is a current-mode precision rectifier and uses a small num- ber of transistors (including bias voltage generators), how- ever, this circuit requires precise threshold voltage extrac- tors and bases itself on the concept that MOS transistors are OFF when the magnitude of gate-source voltage difference is less than the threshold voltage ( V TN or V TP ). This is of course never the case for practical MOS transistors and sub- threshold conduction can lead to large errors in the output if the input signal is of small amplitude.