Technique for controlling the slope of a periodic waveform

摘要

A circuit for forming a substantially periodic signal having a linear relationship between amplitude and time over a portion of its period, wherein a slope in the linear portion is controllable. A transconductance amplifier has a gain which is controllable depending upon a level of biasing current. A capacitor is coupled to an output of the transconductance amplifier wherein a voltage level on the capacitor defines the periodic waveform. Logic signals coupled to inputs to the transconductance amplifier control a direction of current flow from the transconductance amplifier to charge and discharge the capacitor. The biasing current is controllable to control a slope of the periodic waveform. In the preferred embodiment, the invention is used in conjunction with a circuit for forming pulses centered about positive zero crossings of a sinusoidal signal. The biasing current to the transconductance amplifier has two components. A first component of the biasing current is constantly supplied and a second component of the biasing current is selectively supplied. Therefore, the slope of the waveform may have one of two values depending upon whether or not the second component of the biasing current is selected to increase the biasing current of the transconductance amplifier.