Fully Balanced Voltage Differencing Buffered Amplifier and its Applications Viera Biolkova and Zdenek Kolka Dept. of Radio Electronics FEEC, Brno Univ. of Technology Brno, Czech Republic biolkova@feec.vutbr.cz Dalibor Biolek Dept. of EE & Dept. of Microelectronics FEEC, Brno Univ. of Technology, & FVT, Univ. of Defence Brno, Czech Republic dalibor.biolek@unob.cz Abstract—An active circuit element, namely Fully Balanced Voltage Differencing Buffered Amplifier (FB-VDBA), is introduced. Its input stage is composed of a fully-differential operational transconductance amplifier (OTA). Voltage buffer is connected to each OTA output. Several applications are proposed which demonstrate the element’s versatility. The results of SPICE simulation and measurements on experimental specimen are included. I. INTRODUCTION A number of active elements for analog signal processing, based on various principles, have been proposed. Their detailed review is given in [1]. Some of them were designed such that the original topology was generalized to a topology with differential inputs or outputs, or to fully balanced structures. Two motivation factors exist for such a generalization: 1) Increasing the universality of the element and extending the area of its potential applications. 2) Resistance to external noise sources, particularly increased immunity of analog subcircuits to digital noise and interference. The Differential Voltage Current Conveyor (DVCC) [2], a generalization of conventional second- generation current conveyor CCII [3], is a typical representative of Item 1. Similarly, Item 2 can be represented by the Fully Differential Current Conveyor (FDCCII) [4], sometimes also called the Fully Balanced CCII (FBCCII) [5]. The well-known commercial integrated instrumentation operational amplifiers with differential structures [6] are based on the so-called three-OpAmp structure [7]. Other examples of the generalization of classical structures of active elements to their differential versions are summarized in [1]. In [1], the circuit principle called VDBA (Voltage Differencing Buffered Amplifier) is proposed as an alternative to the existing CDBA (Current Differencing Buffered Amplifier) [8]. The input stage of VDBA is composed of the differential-input OTA. The voltage buffer is connected to the OTA current output. Note that this structure is semi-differential. A method of augmenting the voltage buffer by an inverting output is also mentioned in [2], with the corresponding abbreviation DOBA (Differential Output Buffered Amplifier). Replacing the voltage buffer in the VDBA by the DOBA yields a fully differential circuit element. According to the methodology in [1], such an element should be specified as VDDOBA (Voltage Differencing Differential Output Buffered Amplifier). A specific drawback of the VDDOBA consists in the necessity to implement both the voltage buffer and the inverter. Among other shortcomings, it implies a more complicated circuit structure. Therefore, another solution is proposed in this paper, which is based only on voltage buffers, concurrently providing more versatility than VDDOBA. The latter was the main motivation factor for designing this new circuit element. To differentiate it from VDDOBA, it was termed FB-VDBA (Fully Balanced VDBA). II. FULLY BALANCED VDBA The proposed schematic symbol and behavioral model of the FB-VDBA are in Figs 1 (a) and (b). The model can be described by the following set of circuit equations: FB-VDBA v+ z- + z- I w+ z- V V w+ V v- w- z+ - V z+ I w- V z+ V 1 1 FB-VDBA z+ V z- V + V - V w+ V w- V ) ( - + - V V g m (a) (b) Figure 1. (a) Schematic symbol, (b) behavioral model of FBVDBA. ⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ - - = ⎟ ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ - + - + - + - + z z m m m m w w z z V V V V g g g g V V I I 1 0 0 0 0 1 0 0 0 0 0 0 . (1) 978-1-4244-4480-9/09/$25.00 ©2009 IEEE 45