Post-Deflection Acceleration (PDA) is a term often used in the context of cathode-ray tube (CRT) based oscilloscopes, which are instruments used to visualize and analyze electronic signals. In a CRT, an electron beam is generated and deflected to produce a visual representation of a signal on the screen.
When an electron beam in a CRT is deflected to move across the screen to draw a waveform, it takes a certain amount of time to accelerate from one deflection position to another. This acceleration and deceleration time can affect the accuracy and fidelity of the displayed waveform, especially at higher frequencies.
PDA refers to the phenomenon where the electron beam experiences a small acceleration after it has been deflected to a new position. This acceleration can cause the electron beam to overshoot the intended position briefly before settling down. This overshoot can introduce distortions in the displayed waveform, particularly in high-frequency signals.
To mitigate the effects of PDA, modern oscilloscopes employ various techniques, such as:
Bandwidth Limiting: By reducing the bandwidth of the oscilloscope, high-frequency components that could be affected by PDA can be attenuated, reducing the impact of overshoot.
Signal Conditioning: Some oscilloscopes provide options for signal conditioning that can compensate for the PDA effects and correct the displayed waveform.
Advanced Signal Processing: Sophisticated digital signal processing algorithms can be used to correct or compensate for PDA-induced distortions in the displayed waveform.
Higher-Quality CRTs and Display Technologies: Advancements in display technology, including the transition from CRTs to digital display technologies like LCDs and LEDs, have reduced the impact of PDA on waveform accuracy.
It's worth noting that with the advancement of digital oscilloscopes and display technologies, PDA is less of a concern in modern instruments compared to older analog CRT-based oscilloscopes. However, understanding the concept of PDA can still be important when working with older equipment or when analyzing historical data.