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LEFT-ALIGNED AND CENTER-ALIGNED PWM SIGNAL GENERATION IN A COMMON APPARATUS

IP.com Disclosure Number: IPCOM000008208D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-28
Document File: 4 page(s) / 149K

Publishing Venue

Motorola

Related People

Benny Rosen: AUTHOR [+2]

Abstract

There is a need in modem electronics to have left-aligned or center-aligned pulse width modula- tion PWM signals. But, in some situations it is desirable to be able to easily change from one to another. It is wasteful of integrated circuit (IC) real estate to provide separate PWM generators, as has been the case in the past. Therefore there is an ongoing need to have a PWM signal generator capable of producing either or both left-aligned or center-aligned PWM signals. The present invention provides this combination of features.

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MO-LA Technical Developments

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LEFT-ALIGNED AND CENTER-ALIGNED PWM SIGNAL GENERATION IN A COMMON APPARATUS

by Benny Rosen and Elchanan Sharon

  There is a need in modem electronics to have left-aligned or center-aligned pulse width modula- tion PWM signals. But, in some situations it is desirable to be able to easily change from one to another. It is wasteful of integrated circuit (IC) real estate to provide separate PWM generators, as has been the case in the past. Therefore there is an ongoing need to have a PWM signal generator capable of producing either or both left-aligned or center-aligned PWM signals. The present invention provides this combination of features.

  An advantage of the present invention is its efficiency in implementing the multiple modes and fulfilling the "special cases" (see below) in a flexible way, with the minimum devices. The invented arrangement uses a state machine where PWM phase generation is simple and regular and can be duplicated to many channels. This approach also simplifies routing among control and structure (data-path) areas in the electronic module in which the PWM signals are employed.

  Figure 1 is a left-aligned PWM output-mode generator. It is based on a single set-reset (S-R) flip- flop (FF), where a change of PWM output phase is based on Setting or Resetting according to a control signal from a Duty or Period comparator against a running up-counter. An g-bit PWM counter runs at the rate of the selected clock. The counter compares two registers, a duty register and a period register.

When the PWM counter matches the duty register the S-R FF changes state thereby causing the PWM output to also change state. A match between the

PWM counter and the period register resets the FF and the PWM counter.

  Figure 2 is a center-aligned PWM output mode apparatus. In this case the S-R FF functionality is changed to a Toggle (T) FF, and a reversible up-down counter is used. The counting direction is based on "Compare Period" events and the PWM

phase is changed on "Compare Duty" events. In the Center-Aligned-Output Mode (CAOM) the counter operates as an up-down counter and compares the

Duty Register and the Period Register. When the PWM counter matches the Duty Register a Toggle
(T) flip-flop changes state, thereby causing the PWM output to also change state. A match between the PWM counter and the Period Register changes the counting direction from up-count to down- count. When the PWM counter reaches zero, the counter direction changes from down-count to...