DC offset correction for use in a direct-conversion radio architecture

A radio receiver, comprising:

• a receiving stage configured to receive a radio signal;
• a first mixer stage operable to downconvert the radio frequency signal to a first intermediate frequency in-phase signal and a first intermediate quadrature phase signal;
• first and second low pass filters configured to receive and low pass filter the first intermediate frequency in-phase and quadrature phase signals;
• a second mixer stage operable to upconvert the filtered first intermediate frequency in-phase and quadrature phase signals and provide a second intermediate frequency in-phase signal and a second intermediate frequency quadrature phase signal;
• a summer operable to subtract the second intermediate frequency quadrature phase signal from the second intermediate frequency in-phase signal to provide an integrated signal;
• an automatic gain control stage coupled to the summer and operable to amplify the integrated signal;
• an analog-to-digital converter operable to convert the amplified integrated signal to a digital signal;
• a demodulator operable to demodulate the digital signal;
• and
• delay measurement means for determining a delay vector from inputs of the low pass filters to an output of the demodulator.

A method of determining a signal delay between inputs of first and second low pass filters of a dual mixer stage radio receiver and an output of the receiver's demodulator, the method comprising the steps of:

• applying a first known voltage to an input of an in-phase mixer of the second mixer stage;
• applying a second known voltage to an input of a quadrature phase mixer of the second mixer stage;
• setting the gain of an automatic gain control stage, coupled to the second mixer stage, to a full gain;
• measuring first in-phase and first quadrature phase components at the output of the demodulator;
• decreasing the gain of the automatic gain control stage by a predetermined amount if the value of each first component is greater than a predetermined maximum threshold value;
• storing the first in-phase and quadrature phase components if the value of each component is less than the predetermined maximum threshold value;
• applying the negative of the first known voltage to the input of the in-phase mixer;
• applying the value of the second known voltage to the input of the quadrature phase mixer;
• measuring second in-phase and second quadrature phase components at the output of the demodulator;
• decreasing the gain of the automatic gain control stage by a predetermined amount if the value of each second component is greater than the predetermined maximum threshold value;
• storing the second in-phase and quadrature phase components if the value of each second component is less than the predetermined maximum threshold value;
• and
• using the first and second quadrature phase components to compute the signal delay..

A method of compensating for DC offset voltages present at an input of a low noise amplifier of a dual mixer stage radio receiver, the method comprising the steps of:

• determining a signal delay between an output of a second mixer stage of the dual mixer stage radio receiver, said signal delay characterizing in-phase and quadrature phase components of the DC offset voltage present at the input of the low noise amplifier;
• using the determined signal delay to separate and define digital representations of the in-phase DC offset voltage component and the quadrature phase DC offset voltage component;
• making the digital representation of each of the in-phase and quadrature phase components more positive or more negative if it is more negative or more positive than a predetermined minimum threshold or maximum threshold;
• and
• performing the above sequence of steps a predetermined number of times to reduce the DC offset voltage at the input of the low noise amplifier.

A method of setting signal levels of in-phase and quadrature phase components of a radio receiver between a minimum threshold voltage and a maximum threshold voltage, the method comprising the steps of:

• (a) setting the gain of an automatic gain control to a gain value at which the signal levels of the in-phase and quadrature phase components are less than or equal to the maximum threshold voltage;
• (b) comparing the signal levels of the in-phase and quadrature phase components to a predetermined minimum threshold value;
• (c) increasing the gain of the automatic gain control stage by a predetermined amount;
• and
• (d) repeating steps (b) and (c) until the signal levels of the in-phase and quadrature phase components are greater than or equal to the predetermined minimum threshold value.

A method of compensating for DC offset voltages at inputs of in-phase and quadrature phase low pass filters of a dual mixer stage radio receiver, said method comprising the steps of:

• determining a signal delay vector between the inputs of the low pass filters, said signal delay vector characterizing in-phase and quadrature phase components of DC offset voltages at the inputs of the low pass filters;
• using the signal delay vector to separate and define in-phase and quadrature phase multiplication factors associated with the in-phase and quadrature phase DC offsets;
• incrementally adjusting the signal level of the in-phase component to a more positive or more negative value if the in-phase multiplication factor has a negative or positive value, respectively;
• and
• incrementally adjusting the signal value of the quadrature phase component to a more positive or more negative value if the quadrature phase multiplication factor has a negative or positive value, respectively.