Analog Integrated Circuits and Signal Processing, 17, 157±169 (1998) # 1998 Kluwer Academic Publishers, Boston. Manufactured in The Netherlands. A High-Frequency Field-Programmable Analog Array (FPAA) Part 2: Applications EDMUND PIERZCHALA AND MAREK A. PERKOWSKI Department of Electrical Engineering, Portland State University, Portland, OR 97207-0751 edmundp@ee.pdx.edu, mperkows@ee.pdx.edu Received August 2, 1996; Accepted November 10, 1997 Abstract. This paper presents a variety of applications of an FPAA based on a regular pattern of signal-processing cells and primarily local signal interconnections. Despite the limitations introduced by local interconnections, the presented architecture accommodates a wide variety of linear and nonlinear circuits found in many signal processing systems. Thus it effectively proves that it is possible to improve the performance of an FPAA by means of constraining the interconnection pattern, without signi®cantly limiting the class of circuits it can implement. Key Words: programmable circuit, analog signal processing, ®lter, phase-locked loop (PLL), multi-valued logic, fuzzy logic 1. Introduction A companion paper [24] presents an FPAA archi- tecture based on primarily local signal interconnections and a simple analog signal proces- sing cell design. The purpose of this paper is to demonstrate that architecture limitations for the sake of high-frequency performance do not substantially limit the ¯exibility of the FPAA, as measured by the number of different classes of circuits that can be implemented in it. A wide variety of circuits from different classes have been selected in order to demonstrate that a carefully designed FPAA architecture can accommo- date them all. This is not to say that one FPAA circuit would suf®ce for all such applications. Rather, a family of circuits based on a common architecture would be used. For instance, one design might be used to implement linear ®lters, adaptive ®lters, etc., another one to implement matrix operations, arti®cial neural networks, yet another one for fuzzy logic. The selection of applications in this paper serves to demonstrate how a single architecture can be used across many application domains. The paper is organized as follows. Section 2 presents linear ®lters. Section 3 shows examples of nonlinear circuits, such as rank ®lter and phase-locked loop (PLL). Section 4 presents examples of circuits for matrix operations in real time. Finally, Section 5 shows how FPAA can be used to implement multi- valued and fuzzy logic functions. 2. Linear Filters Fig. 1 shows an electrical schematic of an eighth- order elliptic band-pass ®lter realized as an OTA-C 1 ladder. This schematic results from the so-called OTA-C simulation [25] of an RLC prototype based on the design presented in [29]. This is a voltage-mode circuit, since each OTA takes a voltage signal as input, and although it produces a current signal, this current is always turned into voltage, either by the integrating operation of a capacitor, or by another OTA with a feedback connection, which is equivalent to a resistor. This is so because eventually each signal created in this circuit is fed to some OTA (which can accept only voltage-mode signals at the input), or is connected to the output terminals, which also require a voltage- mode signal. This circuit, and other voltage-mode circuits, can be realized in an equivalent current-mode form in the structure of the FPAA discussed here in [24]. The network of the ®lter seems to exhibit little regularity, or locality of connections. Both can be appreciated best when the graph of connections of the ®lter is drawn (Fig. 2). Each pair of wires carries one differential signal, and it is represented as a single