How to control DC voltage and current?
RF Power amplifier measurements can be particularly challenging when dealing with multistage circuits with several ports available for DC power supply control.
IQSTAR allows the DC power supply remote control of up to 20 accesses with associated DC or pulsed voltage and current measurements from the power supplies or using DC precision multimeters and oscilloscopes for pulsed current measurements when the RF signal is pulsed by an RF pulse modulator.
It is very easy to enter various and numerous DC power supply settings for the software GUI without any specific programming skills.
On RF Power amplifiers, different accesses can be available to supply the transistors, Gate bias, Drain bias n°1, Drain bias n°2, and so on, such as in a Doherty RF Power Amplifier for instance.
IQSTAR allows custom labeling of each instrument and its associated DC parameters to simplify the biasing procedure of multistage circuits and the proper recording of the data into the measurement file.
How to Calculate a Voltage Drop Across Resistors ?
It is a must-have to measure accurate DC voltages at the Device Under Test reference plane (DUT), whatever the current consumption. Because the current can flow through a cable with a parasitic serial resistance or through a shunt resistor for differential current measurements, the voltage drop across the serial or possibly parallel resistors must be taken into account to measure the true voltage at the DUT bias access.
A resistive network can also be configured into the IQSTAR DC power supply user interface to de-embed the measurements and the voltage settings to the DUT reference plane.
In addition, customized formulas can be defined to calculate specific DC power consumption values of the RF Power Amplifier if provided with several DC ports.
How to Measure DC or Pulsed Current ?
DC current can be measured simply by reading back the DC current from the DC Power supply through remote control. Nevertheless, it is preferable to use precision DC multimeters plugged in series on the DC path when high current measurement accuracy is needed. IQSTAR enables a seamless DC setup configuration when DC power supplies and DC voltage and current multimeters are used. An oscilloscope can also be used to measure both DC / Pulsed Voltage and Current. Contact us to check the oscilloscope’s drivers, which are available.
How to Synchronize Pulse Measurements ?
When dealing with complex setups to characterize RF power amplifiers in pulsed conditions, it is easy to face the issue of instrument synchronization, especially when using different instruments from different vendors and different generations. For example, some RF sources can generate a fixed output synchronization signal with 50nsec width, but most of the triggered instruments like Power Meters; DMMs… have a minimum trigger hold-off timing of 1usec, resulting in a bad synchronization and wrong measurements, as well as software timeouts.
In this case, it is recommended to advantageously use a Trigger Box with the RF Modulator to help build a robust bench for Pulsed Characterization of Power amplifiers.