FREMONT, Calif. — Speeding up analog circuit simulation is the mission of EDA startup Anasift Technology Inc. (Fremont, Calif.). The company's first commercial offering, which will be introduced at the Design Automation Conference (booth 12), is an analog behavioral-modeling tool called Anascope that relies on "symbolic analysis." Later, Anasift hopes to weigh in with an analog synthesis tool.

"Systems-on-a-chip are incorporating more mixed-signal technology," said Anasift founder Jer-Jaw ("J.J.") Hsu. "But the bottleneck is analog."

Anascope is especially useful for ac behavioral modeling, he said — amplitude response over frequency, determining poles and zeros for filters, and attenuation frequencies for RF circuit elements. But Hsu believes the technology can be adapted to analog-design optimization and even analog-circuit synthesis.

The key to circuit optimization, he said, is an interactive response from the analog-simulation tools. If behavioral digital models can be adapted to "what-if" experimentation, said Hsu, why not analog?

The Anascope simulator provides dramatic speedups over Spice, the universally used simulator, though it is not meant as a replacement, said Hsu. Because of the speed with which it will return results, Anascope can be used as a front-end design aid, as a means of optimizing analog circuit paths or component values to increase frequency response or reduce power consumption. Spice, in turn, retains its value as a back-end verification tool for a completed design.

The key to Anascope's performance is symbolic analysis, a mathematical formulation that reduces the complexity of nodal analysis without decreasing its accuracy. Anascope calculates simplified transfer functions, simplified pole/zero expressions and reduced Laplace variables. In addition to describing transfer functions, Anascope can be used for root-locus analysis, among other things. The symbolic formula calculated by Anascope is based on analog circuit-device parameters. The extracted formulas provide information on how these parameters interact to affect the analog circuit functions. Hsu maintained that this information on the relationship between variables is more useful than Spice outputs, which too often look like nothing more than "a bunch of numbers" to the designer.

Hsu was careful to distinguish between between "symbolic" and "numeric" computations. Spice is numeric; that is, its output is numbers. Anascope is symbolic; its output is closed-form formulas. (A form of symbolic analysis powers the popular DSP simulator MatLab, from The MathWorks.)

In overly simplified terms, symbolic math is much like DSP algorithm development: it effectively reduces a series of open-ended matrix equations into a more-simplified transfer function that can then be represented as algebraic equations.

Like Spice, Anascope is math-intensive. Circuit elements are treated as "black boxes" between inputs and outputs. The transfer function is calculated from performance parameters provided by the user. An op amp, for example, is treated as a closed-loop gain block (Av = -Gi/Gf) operating at low frequencies.

This formula can be expanded to provide progressively more levels of detail, like the closed-loop voltage gain from dc to 100 kHz, or the symbolic pole for a gain-bandwidth product expression. Hsu suggested that parameters can be extracted from existing Spice models or analog cell blocks.

Compared with Spice, the computation time is exceedingly fast. The transfer function describing a 32-transistor 741 op amp, for instance, can be extracted in 30 seconds. The compute time is a function of the number of nodes in the circuit, said Hsu. The 741 has 40 modes. An 80-node circuit would take 150 seconds to describe.

Anascope takes a Spice net-list as the input to calculate simplified symbolic transfer functions in closed forms.

Users can then calculate the voltage gain, current gain, input impedance, output impedance, trans-admittance and trans-impedance from any two input nodes to any two output nodes of the circuit.

Tentative pricing for the Anascope, which runs in the Unix environment, is $79,000.