Fabrication of two independent electrothermal integrators on a single chip [for state-variable filters]

A new layout geometry is given for a rectangular electrothermal circuit (ETC) which produces a single-pole transfer function. Two such circuits, or channels, can be fabricated on a single chip by using an isotropic etch to cut slots which provide isolation between the channels. By addition of appropriate electronic circuits, each channel can be used as an integrator and hence as a building block for a state-variable filter. Measured isolation between channels is 55 dB, and good agreement is obtained between measured and calculated magnitude and phase response of each channel. Good agreement is also obtained between measured and calculated integrator frequency response. Additional external circuitry has been added to produce a bandpass filter with center frequency of 60 Hz and Q of 10; measured and calculated results agree within 3 percent. A new configuration is proposed for integrating on a single chip two ETC integrators and all auxiliary circuits necessary for a second-order filter.