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.