Power Electronics

FPAAs Target High-Volume Analog Applications

A combination of hardware and CAD/CAE software simplifies the design of analog circuits using field-programmable analog arrays (FPAAs) from Anadigm. The newest hardware member of this FPAA family is the AN120E04, intended for high-volume applications requiring consolidation of discrete analog functionality. It follows the AN220E04, optimized to enable dynamic reconfiguration — a capability that allows analog functions to be integrated within the system and controlled by the system processor.

These FPAAs depend on the AnadigmDesigner®2 CAD/CAE software to quickly and easily construct complex analog circuits by selecting and interconnecting building-block subcircuits referred to as configurable analog modules (CAMs). Next, you can download the analog circuits derived from AnadigmDesigner2 to the specific FPAA, which will then function as the software-designed circuit. The designer can immediately view the results of the analog circuit design using a signal generator and oscilloscope.

To understand this FPAA design concept, we must examine the hardware's block diagram (Fig. 1). This diagram consists of a 2×2 matrix of four configurable analog blocks (CABs), optimized for both versatility and performance, surrounded by a fabric of programmable interconnect resources.

The contents of on-chip SRAM configuration memory control the configuration and interconnection of the FPAA circuits. These FPAAs serve as a processing platform for analog signals, for which AnadigmDesigner2 is the “compiler” — easing both the assembly of a design and the coupling of the design to a system processor where run-time control is desired. Thus, these second-generation FPAAs provide a new level of device functionality and performance.

Compared with first-generation FPAAs, the Anadigmvortex architecture provides significant new capabilities. A successive approximation register-based A/D converter can be combined with an on-board 256-byte look-up table to provide advanced analog functions. Combined, you can use these features to implement complex, nonlinear analog functions, such as the following:

  • Sensor response linearization
  • Arbitrary waveform synthesis
  • Signal-dependent functions
  • Analog multiplication
  • Signal companding

Furthermore, with the dynamic reconfigurability of the AN220E04, you can time-slice a single device to implement multiple analog functions or reconfigure the device on-the-fly in response to system events, or to maintain precision operation despite system degradation and aging. This results in increased system functionality and longer system life.

This hardware-software approach:

  • Reduces analog design from months to minutes.
  • Handles designs faster than the use of discretes or ASICs.
  • Enables implementation of multicircuit configurations on a single chip.
  • Eliminates the need to source and maintain any multiple product inventories.

The AN120E04 and AN220E04 (Photos 1 and 2) are reconfigurable. The AN220E04 is dynamically reconfigurable; it is optimized so that it can be updated partially or completely while operating. You can reprogram the AN120E04 as many times as desired, but it must first be reset before issuing another configuration data set.

Most of the analog signal processing occurs within the four CABs and is always done with fully differential circuitry. The CABs have access to a single look-up table that offers a new method of adjusting any programmable element within the device in response to a signal or time base. A voltage reference generator supplies reference voltages to each of the CABs within the device and has external pins for the connection of any filtering capacitors.

Four Input Cells provide the ability to connect analog input signals to the outside world. The fourth Input Cell has a special multiplexing feature that allows the connection of up to four unique signal sources. Each Input Cell can pass a differential signal pair directly into the array, or process either single-ended or differential signals using combinations of a unity gain buffer, a programmable gain amplifier, a programmable anti-alias filter, and a special chopper-stabilized amplifier. The chopper-stabilized amplifier is intended specifically for use with signals requiring significant gain and hence ultralow input offset voltages.

Output signals can be routed from within the array out through the Output Cells directly, or through a programmable reconstruction filter and a pair of differential to single-ended converters. In either case, the external world signal is presented as a differential pair. You can also use Output Cells to output a logic level comparator output signal.

The FPAA accepts either an external clock or generates its own clock using an on-chip oscillator and an external crystal. Detection of the crystal is automatic. Using programmable dividers, you can divide the resulting internal clock frequency into four synchronized internal switched capacitor clocks of different frequencies. The clock circuitry can also source any of these four clocks as a chip output.

The contents of Configuration SRAM control the behavior of the CABs, clocks, signal routing, Input Cells, and Output Cells. Behind every Configuration SRAM bit is a Shadow SRAM bit. The Shadow SRAM of the AN220E04 can be updated without disturbing the currently active analog processing. This allows instantaneous on-the-fly modification of one or more analog functions. This dynamic reconfiguration isn't possible with the AN120E04.

FPAA architecture includes a simple yet highly flexible digital configuration interface that works in the standalone mode by connecting to either a common SPI- or FPGA-type serial EPROM. In this mode, after the device powers up, it automatically loads its configuration from the EPROM and begins functioning immediately thereafter.

You can also use the configuration interface to connect directly to a host microprocessor's SPI master port where it presents itself as a SPI slave. In addition, it can be accessed via a microprocessor's external data bus where the microprocessor's write strobe is recognized as an SPI clock, and only a single data bit of the data bus is used for the serial SPI data.

Reconfiguration of all or part of the device is supported in the AN220E04, allowing multiple configurations to be loaded over time, if required. The configuration interface also allows multiple devices to be easily connected to build larger analog processing systems.

Multiple, independent circuits can be constructed and run simultaneously within a single device, each with its own independent inputs and outputs. For example, two completely independent filter networks, each with its own inputs and outputs, can be constructed — the parameters and operation of one completely independent of the other. A single design can span multiple devices.

CAD/CAE

The new and intuitive Windows-based AnadigmDesigner2 software operates on a standard PC and drastically reduces design time compared with an analog ASIC or discrete implementation. In addition, you can update the circuit functionality in real time using automatically generated C-code.

With dynamic reconfigurability, you can reload new device configurations in real time, allowing the device operation to be time-sliced, or manipulate the tuning or the construction of any part of the circuit without interrupting FPAA operation, thus maintaining system integrity.

AnadigmDesigner2 includes prepackaged common analog functions for which the user sets the parameters. Simply by dragging and dropping configurable analog modules (CAMs), designers can create a complete analog system on the FPAA, simulate it immediately, and then download it to the FPAA chip for testing and validation.

A functional simulator is included and facilitates circuit design and experimentation without the need for lab equipment. The simulator features an intuitive user interface and displays time domain results graphically.

Fig. 2, above, shows a typical computer screen presentation employed by AnadigmDesigner 2 to layout an analog circuit. Using a mouse, you can connect device inputs and outputs to the Input Cells and Output Cells. You can also use the mouse to insert additional CAMs stored in the Circuits folder in the software.

Anadigm Inc., Campbell, Calif. CIRCLE 348 on Reader Service Card

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