Filter offset compensation

摘要

Problems arising from a pre-emphasis filter, particularly an infinite-impulse-response filter, in a signal modulator are solved by detecting sequences of the same bit or symbol in a modulation signal and compensating the corresponding d.c. offset in the signal generated by the pre-emphasis filter without real-time feedback. The amount of offset compensation can be defined during design of the modulator or adjusted or calibrated during production. It is not necessary to change the transfer function of the pre-emphasis filter, but only to correct the d.c. offset of the filter output signal.

主权项

1. An electronic signal modulator (400), comprising:
a pulse-shaping filter (102) that receives a digital modulation data signal; a high-pass pre-emphasis filter (104); a phase-locked loop (PLL) (110) that generates a carrier signal modulated by the digital modulation data signal, wherein the PLL has a low-pass frequency response to be compensated by a frequency response of the pre-emphasis filter; a sequence detector (402) configured to detect a sequence of bits of the digital modulation data signal that are the same, wherein the sequence has a length of at least a number N of bits, and the sequence detector generates an output signal based on a sequence detected; an offset compensator (404) responsive to the output signal of the sequence detector and configured to add a compensation value to an output of the pre-emphasis filter; and a summer (406, 106) configured for receiving the output of the pre-emphasis filter and the compensation value and for generating a control signal applied to the PLL.