Browse Prior Art Database

IN-PHASE SQUARE-TO-SINE WAVE CONVERTER

IP.com Disclosure Number: IPCOM000005825D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-09
Document File: 3 page(s) / 145K

Publishing Venue

Motorola

Related People

Gary E. Mueller: AUTHOR [+2]

Abstract

The conversion of a given square wave into a sinusoid of same fundamental frequency is usually, and easily, ac- complished using basic filtering techniques. However, when it is required that the resultant sinusoid have very low distor- tion and be in phase with the input square wave, basic filtering approaches prove not to be a viable solution. A finite delay in response time due to an impulse or step function, is associated with conventional filtering techniques. This response time delay results in a phase-shifted output waveform. The response time delay is also a function of the filter's rolloff. The higher the rolloff, the greater the delay from input to output will be. For a low distortion output, a sharp rolloff is required and hence, a greater delay is added to the resultant output waveform. The scenario for an example of such stringent requirements is demonstrated in its use for a multitransmitter simulcast transmission.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 46% of the total text.

Page 1 of 3

m MOTOROLA Technical Developments Volume 10 March 1990

IN-PHASE SQUARE-TO-SINE WAVE CONVERTER

by Gary E. Mueller and James W. Dejmek

   The conversion of a given square wave into a sinusoid of same fundamental frequency is usually, and easily, ac- complished using basic filtering techniques. However, when it is required that the resultant sinusoid have very low distor- tion and be in phase with the input square wave, basic filtering approaches prove not to be a viable solution. A finite delay in response time due to an impulse or step function, is associated with conventional filtering techniques. This response time delay results in a phase-shifted output waveform. The response time delay is also a function of the filter's rolloff. The higher the rolloff, the greater the delay from input to output will be. For a low distortion output, a sharp rolloff is required and hence, a greater delay is added to the resultant output waveform. The scenario for an example of such stringent requirements is demonstrated in its use for a multitransmitter simulcast transmission.

   For multitransmitter simulcast of binary information, it has been shown 1 that by superimposing a sine wave of specific amplitude, phase, and frequency on the data stream to be transmitted, a maximum-ratio combining diversity effect can be realized in the overlapped region. This superimposing sine wave is to be derived from a clock input (square wave) whose phase has been properly adjusted to achieve the aforementioned effect. The binary information will have a specific phase relationship (i.e. difference) to the input, The integrity of this relationship is to be preserved while deriv- ing the superimposing sine wave from the clock signal. The in-phase square-to-sine wave converter cirmcumvents the delay problems associated with filtering while still providing a very low distortion output waveform.

   The in-phase squareto-sine wave converter is illustrated in Figure 1. Its output is a sinusoidally-enveloped staircase waveform that is in phase (zero degrees of shift) with the input clock signal. The summing amplifier does cause an inversion. If this were not required nor desired, an inverter could be added to the data input of the first shift register.

   Generically, an input square wave of frequency f is clocked through an N-bit shift register at a rate of 2N x f. The outputs have weighted resistors on them and are then tied together and fed to a summing amplifier (to adjust for gain purposes). The resistors are weighted such that the resulting waveform is a staircase closely approximating a sinusoid. A smoothing filter will smooth this waveform while also superimposing it on the data. By superimposing the sine wave on the data at this point, any delay introduced by the summing filter (with respect to the input clock) is subsequently added to the data. The N-bit shift register would inherently cause a 90" phase shift. However, by inverting the last N/2 outputs, this phase shift is...