Automatic frequency control circuit

Abstract

Disclosed is an automatic frequency control circuit for correcting the influence of frequency offset in a radio data communication terminal of a scheme in which transmission path characteristics are obtained during the preamble period by narrow-band modulation to equalize the received signal. The automatic frequency control circuit includes, on the transmitter side, a unit for repeatedly transmitting the pattern of a predetermined pseudo noise (PN) signal serving as a preamble signal, on the receiver side, a unit for calculating the phase difference per PN cycle on the basis of the component (real and imaginary part amplitude values) of a PN signal one cycle before that is quadrature-modulated during a predetermined period of the preamble, and the component of a current PN signal, a unit for dividing the phase difference by the number of symbols of one PN cycle to obtain the phase difference (.DELTA..theta.) of the unit symbol, a unit for holding .DELTA..theta. during the burst period, a unit for integrating .DELTA..theta. in units of symbols during data demodulation, a unit for converting the integrated value into real and imaginary part amplitude values, and a unit for correcting the phase of the demodulated received signal on the basis of the obtained real and imaginary part amplitude values.

Dependencies are inferred from the claim text.