Non-linear reference waveform generators for data conversion and other applications

摘要

A machine for generating piece-wise non-linear reference waveforms at low cost, particularly in integrated circuit technologies. The reference waveform can be a distorted sinusoidal waveform such as a truncated sinusoid. Provided that local distortion is low enough in some waveform segments, for instance, in the transitions between saturation levels, parts of the waveform can be used as non-linear reference segments in data converters based on comparison of inputs. The distorted sinusoidal waveform can also be filtered to reduce distortion. In the preferred embodiment of the invention, suitable sinusoids with high or low distortion can be generated using an op-amp configured with a Wien Bridge providing positive feedback and a resistor bridge providing negative feedback. The invention differs from prior art Wien Bridge oscillators in having negative feedback gain that forces the op-amp output into saturation. One filter stage is provided by the positive feedback network itself. Additional filtering can allow further distortion reduction. The specification suggests a cascade of servo-grounded Wien Bridge stages as a simple and efficient approach to the filtering. The invention can be fabricated using a small number of parts which are easy to fabricate with existing integrated circuit technologies such as CMOS, so that low-cost, low-power implementations can be included in mixed-signal chips as parts of A/D converters, D/A converters, or calibration signal generators. The invention is also amenable to massively parallel and shared implementations, for instance, on a CMOS image sensor array chip or on a image display device.