Abstract: A digital potentiometer includes a string of impedance units in series. The string includes identical first and second sets of impedance units whose individual impedance values increment by a power of two. One of a plurality of switches is coupled in parallel with each respective impedance unit. The switches that are coupled to the first set of impedance units receive logical control signals complementary to logical control signals received by the respective switches coupled to the second set of impedance units, so that for every impedance unit of the first set that is bypassed (not bypassed), the identical impedance unit of the second set is not bypassed (bypassed). The string may include only the first and second sets of impedance units, or may include at least one third impedance unit in series with the first and second sets in a multi-stage design.

Abstract: Methods and apparatus for adjusting DC bias of a radio frequency (RF) amplifier for changing operating conditions such as multiple modulation techniques when no RF is present. A digitally controlled voltage source is programmed to maintain the amplifier bias. The voltage source can be a digitally controlled potentiometer. The amplifier's DC output current can be converted to a voltage and compared to a programmable reference representative of the optimal amplifier bias. The comparator output determines a direction to drive the voltage source. A digital clock is enabled to drive the voltage source when no RF is present. Alternatively, the amplifier's output current can be read by a processor that determines the optimal bias. The bias can be written to a data register that sets the voltage on the voltage source. The system automatically compensates for changes in the amplifier's optimal bias due to aging, temperature, and modulation scheme.

Abstract: Methods and apparatus for adjusting DC bias of a radio frequency (RF) amplifier for changing operating conditions such as multiple modulation techniques when no RF is present. A digitally controlled voltage source is programmed to maintain the amplifier bias. The voltage source can be a digitally controlled potentiometer. The amplifier's DC output current can be converted to a voltage and compared to a programmable reference representative of the optimal amplifier bias. The comparator output determines a direction to drive the voltage source. A digital clock is enabled to drive the voltage source when no RF is present. Alternatively, the amplifier's output current can be read by a processor that determines the optimal bias. The bias can be written to a data register that sets the voltage on the voltage source. The system automatically compensates for changes in the amplifier's optimal bias due to aging, temperature, and modulation scheme.