Filter Offset Compensation
AssigneeST-Ericsson SA
InventorJorma Pertti Matero
Life of this patent
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Abstract
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.
Claims12
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 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 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 an output of the pre-emphasis filter and the compensation value and for generating a control signal applied to the PLL.
A method of compensating a frequency response of an electronic signal modulator, comprising:
- high-pass filtering (802) a digital modulation data signal, thereby generating a filtered modulation signal;
- detecting (804) 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;
- selecting (806) a compensation value based on a sequence detected;
- combining (808) the compensation value and the filtered modulation signal, thereby generating a compensated modulation signal;
- and
- generating (810) a carrier signal modulated by the compensated modulation signal.
Dependencies are inferred from the claim text.