Continuous time integrator filter with minimum phase variation, passband Sigma-Delta modulator using this filter

摘要

The filter integrator (1) is used in an enslavement loop of a Sigma-Delta modulator which also comprises an analog-digital converter (2) and a digital-analog converter (3) in the same loop. The filter integrator comprises in particular two resonant cells 6p(1), 6p(4) in the form of parallel LC circuits, a series circuit with alternating amplifiers 12(1), 12(2), 12(3) and filters 11(2), 11(3), a fourth amplifier (12(4) connected to the output, a generator 5s, and a load (7). Each filter 11(2), 11(3) contains three sections, and each section contains two resonant devices, one series and the other parallel. The resonant cells 6p(1), 6p(4) are with low overvoltage and designed to minimize the effect of spectrum folding brought in by the analog-digital converter (2). The functioning of the modulator with closed loop is stable within the following margins +/- 20 degrees in phase, and +/- 3 dB in amplitude. The resonant device comprises a resonator and a resistor, and the transfer function becomes dominant in one or more of the frequency bands. The resonant device is with a phase delay when the function of resistance is dominant in the frequency bands symmetric with respect to the resonant frequency. The resonant device is with a phase advance when the function of resistance is dominant in a frequency band comprising the resonant frequency. The filter is of a higher order, and the resonant devices are assembled in a cascade, in a ladder, or in a balanced bridge. The elements of components are implemented in a piezoelectric substrate, or in the interior of a ceramic case. The resonators are ceramic acoustic wave (SAW), bulk acoustic wave (BAW) or variants such as fundamental bulk acoustic resonator (FBAR), high order bulk acoustic resonator (HBAR) or thin film resonator (TFR), dielectric, or superconductor. The enslavement loop comprises the filter as claimed, and the latent number is strictly greater than 1. The Sigma-Delta pass-band modulator consists of the enslavement loop and comprises an analog-digital converter in the direct route and a digital-analog converter in the return route of the loop. One or more, or all of the elements of components are implemented in a semiconductor, and the filter is implemented in a piezoelectric substrate related to the semiconductor, or in the interior of a ceramic case of the modulator.