Mixed Signal Power Amplifier Test Challenges
Challenge: Changing Power Amplifier Market Dynamics
- More modes + more bands = more measurements
- Increasing time-to-market pressure
- RF instruments test faster and cheaper
Power Amplifier Testing is unique.
It requires fast test time while still implementing on a vast area of mixed signal instruments. A common industry trend is to put multiple PA’s on the same chip. Therefore, a single part may support multiple frequencies or bands. Even within a single band, a part may support multiple modes (IE GSM or EDGE). We control these modes using digital control logic.
Source of DC power is actually one of the hardest requirements of testing a microwave PA. Typical off-the-shelf power supplies are insufficient to meet power requirements for cellular PAs because the device ramps power so quickly that the instantaneous current consumption is very high. Powering a standard GSM or EDGE PA with a typical power supply doesn’t give time for the measurement to stabilize, and therefore a battery simulator is recommended as it minimizes the transient response time.
Mode and Control – Digital Generator
Digital Pattern Control is a newer requirement. Digital control for enable, mode, band, stardards, or other settings are common on PAs. In fact, many speak specific protocol lanuages like SPI, I2C, etc.
Vramp – Arbitrary Waveform
A difficult measurement when controlling an RF PA is the Vramp signal. This controls the gain of the amplifier as the signal shape is critical for performance to make sure the amplifier doesn’t provide to much gain too quickly. Driving the Vramp signal is easier on PXI because the shape of the signal can be easily defined in software, such as LabVIEW.
RF Input – Multiband
RF input to test the PA has several requirements as well. Typically the signal is required to be either a continuous wave, or modulated. It may have a wide range of signal content requirements, as devices use more and more wireless standards. It is common to use a single multi-mode PA for many different standards such as GSM/EDGE, WCDMA/HSPA+, LTE, and 802.11x.
RF Output – Multiband
Typical RF Output measurements include power, efficiency, and modulation analysis. When testing a multi-mode PA, it is typical to use microwave switching to switch various PA outputs to a single RF vector Signal Analyzer. We leverage the tight syncrhonization provided by the PXI platform and easy signal defined implementation provided by the software to achieve these requirements.
Solution: Migrating test bench setup to PXI platform
Modern test architectures require:
PXI platforms address these requirements through:
- PC based technology
- Modular hardware
- Flexible software