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Method for mismatch insensitive PWM-synchronization control

IP.com Disclosure Number: IPCOM000131667D
Original Publication Date: 2005-Dec-10
Included in the Prior Art Database: 2005-Dec-10
Document File: 3 page(s) / 54K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Prediction of Matching errors or mismatch in digital circuits is necessary, especially for self-oscillating PWMs (PWM, Pulse-Width-Modulator). Therefore, it is advantageous to use synchronization control loops in order to detect matching errors and to compensate them. Presently known methods reduce the mismatch of two independent SOPA's (Self-Oscillating-Power-Amplifier) by detecting the timing mismatch and effectuate an output difference of zero by controlling appropriately the delay control input of the delay elements integrated in the SOPA loops. A possible implementation of synchronization loops for tri-level PWM-SOPA consists of: levelshifter, 'Pulse Center of Gravity Detector', charge pump, loop filter and converter. The levelshifter is necessary to convert the high voltage switching signals at the SOPA outputs to a voltage level convenient for further processing. The 'Center of Gravity Detector' extracts the timing screw (T) between the two outputs. A differential charge pump transfers a net charge proportional to T into the passive loop filter, where the average timing error is converted to a differential output voltage. The loop filter output voltage is in turn converted to proportional control currents for the delay elements in the SOPA loops. Nevertheless, the effectiveness of the synchronization control loop is limited by several mismatch sources:

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Method for mismatch insensitive PWM-synchronization control

Idea: Martin Clara, AT-Villach; Dr. Andreas Wiesbauer, AT-Villach

Prediction of Matching errors or mismatch in digital circuits is necessary, especially for self-oscillating PWMs (PWM, Pulse-Width-Modulator). Therefore, it is advantageous to use synchronization control loops in order to detect matching errors and to compensate them. Presently known methods reduce the mismatch of two independent SOPA's (Self-Oscillating-Power-Amplifier) by detecting the timing mismatch and effectuate an output difference of zero by controlling appropriately the delay control input of the delay elements integrated in the SOPA loops. A possible implementation of synchronization loops for tri-level PWM-SOPA consists of: levelshifter, 'Pulse Center of Gravity Detector', charge pump, loop filter and converter. The levelshifter is necessary to convert the high voltage switching signals at the SOPA outputs to a voltage level convenient for further processing. The 'Center of Gravity Detector' extracts the timing screw (∆T) between the two outputs. A differential charge pump transfers a net charge proportional to ∆T into the passive loop filter, where the average timing error is converted to a differential output voltage. The loop filter output voltage is in turn converted to proportional control currents for the delay elements in the SOPA loops. Nevertheless, the effectiveness of the synchronization control loop is limited by several mismatch sources:

1) Mismatch between the two halves of the levelshifter

2) Mismatch between PFD-A and PFD-B (PFD, Phase Frequency Detector) in the 'Center of Gravity Detector'

3) Mismatch between UP- and DOWN-current in the charge pump

4) Mismatch in the loop filter (only for active loop filter)

5) Mismatch in the wiring or driver performance between one of the above mentioned blocks

In the following, a solution is proposed, which uses a chopped charge pump circuit. Figure 1 shows the extension of the charge pump circuit used in known applications. The single PMOS (p-channel metal oxide semiconductor) and NMOS (n-channel metal oxide semiconductor) current-sources are used to generate both UP- and DOWN-currents. If bit swap=0, then IUP=IP1+IN2 and IDOWN=IP2+IN1. If swap=1, then IUP=IP2+IN1 and IDOWN=IP1+IN2. In order to ensure proper charge pump operation if swap=1, the signals UP and DOWN have to be exchanged before arriving the switch...