Digital quadrature amplitude modulator
US4661948A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 12, 1985 |
| Grant date | Apr 28, 1987 |
| Priority date | — |
| Expiry date | Feb 12, 2005 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/365
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
In a quadrature amplitude modulator, two binary, synchronous data signals representing four possible phase states of a carrier signal are sampled and respectively fed into two shift registers comprising part of a finite impulse response lowpass filter. The samples in each corresponding pair of stages in the shift registers are multiplexed at twice the carrier frequency. Each multiplexer output is then added modulo-two to a binary signal at the carrier frequency using exclusive-OR gates. The gate outputs are weighted in a desired fashion and summed and converted to an analog signal which exhibits a preferred spectral shape. This approach enables the quadrature amplitude modulation function to be included within the structure of the finite impulse response lowpass filter. The binary synchronous nature of the input data enables the structure of the filter to be simplified and the number of multiplexers and modulo-two adders to be reduced to a number equal to the number of bits stored from the input sequences. An extension of this basic concept includes higher levels of encoding, specifically the case of sixteen or more possible phase and amplitude states of a carrier signal. The parti…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.