US 12,294,375 B2
Adaptive low-pass filter for zero-crossing detection
Guido Dossi, Monza Brianza (IT)
Assigned to STMicroelectronics International N.V., Geneva (CH)
Filed by STMicroelectronics International N.V., Geneva (CH)
Filed on Sep. 21, 2023, as Appl. No. 18/371,038.
Prior Publication US 2025/0105831 A1, Mar. 27, 2025
Int. Cl. H03K 5/1536 (2006.01); H03H 11/04 (2006.01); H03K 5/156 (2006.01)
CPC H03K 5/1536 (2013.01) [H03H 11/04 (2013.01); H03K 5/1565 (2013.01)] 23 Claims
OG exemplary drawing
 
1. A circuit configured for detection of a zero crossing in a power signal, comprising:
a low-pass filter (LPF) configured to receive an input signal indicative of the power signal and to introduce a phase shift dependent on a frequency of the input signal;
filter circuitry configured to: receive an output of the LPF and to apply a fixed phase shift thereto, and adjust phase and DC offset correction of the output of the LPF based on control signals to produce a filtered output signal; and
control circuitry comprising:
a zero crossing detector configured to receive the input signal and the filtered output signal, detect zero crossings of the input signal and the filtered output signal, assert a digital zero cross signal at each zero crossing, and determine a phase shift and DC offset correction between the input signal and filtered output signal; and
a controller configured to generate the control signals, based upon the phase shift and DC offset correction, such that a total phase shift between the input signal and the filtered output signal is constant and there is a same duty cycle between the input signal and the filtered output signal, thereby providing for accurate zero crossing detection by the zero crossing detector.