Output impedance calibration of integrated switched-mode power amplifiers

An NMR apparatus comprising:

• an NMR coil configured to enclose a sample;
• an integrated switch-mode PA coupled to the NMR coil;
• and
• circuitry for reducing variability of an output impedance of the PA;
• wherein the circuitry comprises (i) a PA driver comprising one or more PMOS components and one or more NMOS components, (ii) a pre-driver for facilitating activation and deactivation of the PA driver, (iii) a passive resistor coupled to the PA driver for splitting the output impedance between the PA driver and the passive resistor, and (iv) a calibration circuit comprising a replica circuit of the PA driver and a load resistor for calibrating an ON resistance of the PA driver so as to provide stable output power levels, the replica circuit comprising one or more PMOS components and one or more NMOS components identical to the components of the PA driver.

A method of reducing variability of an output impedance of an integrated switch-mode power amplifier (PA), the method comprising:

• providing a PA driver having one or more PMOS components and one or more NMOS components;
• providing a pre-driver for facilitating activation and deactivation of the PA driver;
• providing a calibration circuit comprising a replica circuit of the PA driver and a load resistor for calibrating an ON resistance of the PA driver, the replica circuit comprising one or more PMOS components and one or more NMOS components identical to the components of the PA driver;
• adjusting a first number of stripes of the replica circuit such that the ON resistance thereof has a desired impedance;
• and
• adjusting a second number of stripes of the PA driver based at least in part on the adjusted first number of stripes to provide the desired impedance.