Apparatus and method for compensating for DC-offset in direct conversion receiver of wireless communications system

A direct conversion receiver of a wireless communications system, the receiver comprising:

• a voltage control oscillator for generating a local oscillation signal having the same frequency as an input signal;
• a frequency converter for combining the input signal with the local oscillation signal;
• a first compensator for determining a first direct voltage offset generated due to a leaked local oscillation signal flowed into the frequency converter, for feeding back a magnitude of the determined first direct voltage offset to the frequency converter, and for compensating for the first direct voltage offset;
• a first variable gain amplifier for performing a first modem associated offset compensation;
• a first register for storing the fed back magnitude of the first direct voltage offset for the first variable gain amplifier:
• a low pass filter positioned in a rear end of the first variable gain amplifier;
• a second compensator for compensating for a second direct voltage offset by feeding back a magnitude of the second direct voltage offset generated in the low pass filter to the low pass filter;
• a second variable gain amplifier for performing a second modem associated offset compensation;
• a second register for storing the fed back magnitude of the second direct voltage offset for the second variable gain amplifier;
• an output buffer positioned in a rear end of the second variable gain amplifier;
• and
• a third compensator for compensating for a third direct voltage offset by feeding back a magnitude of the third direct voltage offset generated in the output buffer to the low pass filter,
• wherein the first variable gain amplifier is positioned in a rear end of the frequency converter, connected to the first register, and performs the first modem associated offset compensation after the compensation for the first direct voltage offset by the feedback using the fed back magnitude of the first direct voltage offset stored in the first register, and
• the second variable gain amplifier is positioned in a rear end of the low pass filter, connected to the second register, and performs the second modem associated offset compensation using the fed back magnitude of the second direct voltage offset stored in the second register.