4.3 Commercial FPAA products

4.3 Commercial FPAA products

Realising their significance and market, industry has quickly come into the FPAA business. Though the programmable analogue concept has been around for only about ten years [1], several FPAA products have already been commercially available from different companies. With the current commercial and research trends in the area of reconfigurable analogue devices, more and more high-performance FPAAs will certainly appear in the future.

Some typical commercial FPAAs are presented in Table 4.1 with some comparative information about different types in terms of bandwidth, circuit techniques, IC technology and applications. As examples, we will illustrate three FPAA products from Lattice, Zetex and Anadigm, respectively, in the following sections.

Table 4.1: Commercial FPAAs

Company	Bandwidth	Circuit technique	IC technology	Applications
Motorola MPAA [13, 14, 21]	200 kHz	Switched-capacitor	CMOS	General signal processing
IMP EPAC [22]	125 kHz [2], 150 kHz [12]	Switched-capacitor	CMOS	Signal conditioning or monitoring
Lattice ispPAC [23]	1.5 MHz	Continuous-time (op-amp-RC)	CMOS	Signal processing and conditioning
Zetex TRAC [24]	4–12 MHz	Continuous-time (log domain)	Bipolar	General signal processing
Anadigm FPAA [25]	10 MHz	Switched-capacitor	CMOS	Signal processing and conditioning

4.3.1 Lattice semiconductor's programmable analogue circuits (ispPAC)

Lattice has released commercial FPAA-like op-amp-RC products. Different ispPAC family products are available for different kinds of application like lowpass filters, analogue frontends, signal conditioning, and control loop applications. The block diagram of ispPAC20 is shown in Figure 4.4 [23], all of the ispPAC family devices having almost the same basic blocks as ispPAC20.

Figure 4.4: Block diagram of ispPAC20

The ispPAC device has a number of programmable IAs (instrumentation amplifiers), OPs (operational amplifiers), and CPs (comparators). All of them can be configured to connect existing circuits. IspPAC devices also come with 8-bit multiplexed DACs, and different ranges of reference voltage are also available. Different ispPAC devices have different bandwidths dependent on application criteria. The maximum available bandwidth is 1.5 MHz in ispPAC30. All ispPAC family products can be reconfigured on the fly, by exchanging configuration bits between the SDRAM configuration shift register and an on-chip memory.

4.3.2 Zetex semiconductor's TRAC (totally reconfigurable analogue circuit)

Fast Analogue Solutions (FAS) of Zetex has introduced the totally reconfigurable analogue circuit (TRAC), a continuous-time, log-domain bipolar design operating at up to 12 MHz. The TRAC includes 20 CABs, organised in two rows of 10 CABs, each capable of implementing one of the following functions: log, anti-log, noninverting pass, addition, negating pass, op-amp, and half-wave rectification. The interconnection network is hard-wired, as shown in Figure 4.5 [17, 24]. Topological programming is implemented by tuning CABs off, and by external wiring of the pins. By tuning a CAB off, its inputs and outputs are electrically disconnected, allowing the designer to use the output as an input to the subsequent CAB. Amplifier gain is determined by using off-chip resistors. Configuration of the CABs is accomplished using a 60-bit string. Once more, a CAD tool is used to configure the TRAC; the CAD tool includes a simulator to simulate a circuit before being downloaded on to the FPAA IC. FAS advocates a computational approach to analogue circuit design, where circuits are designed with their functionality in mind (a top-down approach), rather than the underlying circuitry (a bottom-up approach).

Figure 4.5: Part of FAS TRAC020 array architecture

4.3.3 Anadigm field programmable analogue array (AN10E40)

Anadigm has released a CMOS switched-capacitor FPAA design called AN10E40. This FPAA architecture, organised as an array of CABs, is illustrated in Figure 4.6 [25]. The AN10E40 consists of a 4 5 matrix of fully configurable switched-capacitor cells, enmeshed in a fabric of programmable interconnect resources. These programmable features are directed by an on-chip SRAM configuration memory. The SRAM configuration memory is initialised on power-up via an off-chip serial PROM or through a microprocessor peripheral interface. The SRAM block that controls routing connections and CAB behaviour is loaded during configuration. Configuration typically occurs at power up as an automatic process but can of course be re-initiated at any time. The ability to re-configure the part at any time gives the user flexibility in system design. Programmable capacitor banks and local switching in both the input paths to the op-amp and a programmable capacitor bank in the op-amp's feedback path provide all the resources required to implement a very large number of analogue processing circuits. AN10E40 comes with configurable clocks which can be used up to 40 MHz, although the switched capacitors and switches allow this FPAA to work up to 10 MHz bandwidth. AN10E40 comes with PC-based CAD tools and quite a few ready-made ipMODUAL libraries [25].

Figure 4.6: Block level view of the AN10E40 array