Digital Doherty schematics
The basic test set-up comprises an SMW200A signal generator, FSW signal analyzer and HMP power supply. This configuration supports testing to 20GHz. For testing up to 40GHz, a solution based on the SMW + SGMA is used. Testing the Doherty Amplifier as a dual-input device requires a few additional steps in the calibration phase, before insertion of the dual-input DUT.
The measurement algorithm may be rapid or more exhaustive. It may be programmed to seek out optimum values directly for desired parameters. It might equally be configured just to characterize over a wide sweep range of parameters, for example, input power, amplitude and phase balance, bias points, etc.
In a simple case, the engineer might want confirmation merely of the best-case quantities, and their relative amplitude/phase balance values. In another case, the engineer might like a more detailed sweep, for example, to enable a sensitivity analysis or a more rigorous solution space search.The post-processing of these results can be as simple or sophisticated as the user wishes.
Multiple input sources calibration
One method for calibrating the multiple input sources is to use a power combiner (ideally in-phase and isolated). By detecting the cancellation case, the accuracy of amplitude, phase and time coherence can be maximized. Better still, this enables the use of a representative test signal. With a stable calibration, whose dual path plane is extended to the DUT inputs, the measurement may be performed.
