Resonant MEMS mirror parameter estimation
A resonant scanning mirror includes a sensor to provide position information. A parameter estimation circuit estimates parameters from the position information. The parameter estimation circuit includes wideband analog circuits that have poles far removed from the resonant frequency of the scanning mirror. The parameter estimation circuit also includes an analog-to-digital converter that samples at a high sample rate, and digital filters that exhibit near perfect linearity.
1. A scanning laser projector comprising:
at least one source of laser light;
a scanning mirror to reflect the laser light, the scanning mirror having a position sensor to provide a position feedback signal in response to movement of the scanning mirror at a resonant frequency; and
a parameter estimation circuit to predict a position of the scanning mirror between zero crossings of the position feedback signal, the parameter estimation circuit including a resonant analog anti-aliasing filter having a 3 dB bandwidth of at least ten times the resonant frequency of the scanning mirror, an analog-to-digital converter, and a digital filter chain to isolate spectral content at the resonant frequency of the scanning mirror.
2. The scanning laser projector of claim 1 wherein the analog anti-aliasing filter has a 3 dB bandwidth at least 30 times the resonant frequency of the scanning mirror.
3. The scanning laser projector of claim 1 further comprising a unity gain wideband buffer coupled between the position sensor and the analog anti-aliasing filter.
4. The scanning laser projector of claim 1 wherein the digital filter chain comprises a digital anti-aliasing filter.
5. The scanning laser projector of claim 4 wherein the digital filter chain further comprises a digital down-sampler, a digital bandpass filter, and a digital up-sampler.
6. The scanning laser projector of claim 1 further comprising a zero crossing estimator responsive to the digital filter chain.
7. The scanning laser projector of claim 1 further comprising a peak amplitude estimator responsive to the digital filter chain.