Q.
For a Digital Step Attenuator (DSA), what is step error and state error?
A.
Step error: The step error is the error in stepping between consecutive states.
- For a 0.5dB LSB attenuator in an ideal world (with 0dB step error), the delta between any two successive states would be 0.5dB.
- Using ADRF5720 as an example to illustrate step error with an example:
- For 9kHz to 10GHz, the delta between any two successive states can be 0.5dB ± 0.15dB → 0.35dB to 0.65dB typical. This gets worse as we go higher in frequency.
State Error: The state error is the error between the desired state vs measured state.
- For a 0.5dB LSB attenuator in an ideal world: with 0dB state error, the 5dB state will measure (5dB + insertion loss) or the 30dB state will measure (30dB + insertion loss).
- Continuing the example from above:
- For 9kHz to 10 GHz, the typical state error is specified as: ±(0.15 + 1% of state). Say you’re interested in the 30dB state. 1% of 30dB = 0.3dB. This makes the range:
±(0.15 + 0.3dB) → ± 0.45dB → 29.55dB to 30.45dB.
Please note: state error is calculated from data that is normalized to the insertion loss state. Therefore, what you would actually measure would be 29.55dB+IL to 30.45dB+IL when choosing the 30dB state.