Parabolic current generator for use with a low noise communication bus

Abstract

A parabolic current generator is provided for use with a waveshaping circuit for producing a sinusoidally increasing bus output voltage signal in response to the rising edge of a data input signal, and a sinusoidally decreasing bus output voltage signal in response to a falling edge of the data input signal. The parabolic current generator provides a current that increases parabolically in response to the rising or falling edge of the data input signal and that decreases parabolically when the bus output voltage signal reaches one-half of its intended full voltage swing or falls below one-half of the full voltage swing to respectively produce the sinusoidally increasing and decreasing voltage at the bus output. The parabolic current generator includes an operational amplifier having an integrating capacitor connected between its non-inverting input and its output. A field effect transistor is connected to its inverting input and has an impedance sized to minimize the capacitor value.