Abstract
In this paper, we propose a polar coordinate transformation in real time
using the COordinate Rotation DIgital Computer (CORDIC) algorithm in order
to realize an electronic predistorting transmitter with a practical circuit
implementation. The proposal enables a dual-drive Mach–Zehnder
modulator (DDMZM) to use vector in-phase/quadrature-phase (I/Q) modulation
to generate predistorted complex electronic fields. The basic theory of
coordinate transformation and the CORDIC algorithm are explained in detail.
The expected dispersion compensation performance for 40-Gb/s differential
quadrature phase-shift keying (DQPSK) is evaluated by numerical simulations.
The required number of iterations of the CORDIC algorithm and its impact on
signal quality are also clarified. Simulation shows that only seven
iterations are required to achieve signal quality sufficient for
predistortion transmission. A practical size of 6.9-M gates is estimated to
be sufficient for the large scale integration (LSI) implementation for
40-Gb/s DQPSK systems.
© 2009 IEEE
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