Lesson 21 Flashcards — Signal Conditioning#
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1. Name the three pitfalls signal conditioning addresses.
Aliasing (a frequency problem), clipping (signal too big), and wasted dynamic range (signal too small).
2. Where must conditioning happen relative to the ADC?
Before it, always. Both aliasing and clipping destroy information at the moment of conversion; afterward is too late.
3. How do you specify an anti-aliasing filter?
A low-pass filter with \(f_\text{cutoff}\) just above the highest frequency you care about, then choose \(f_s \geq 2f_\text{cutoff}\) — with margin. A real first-order R-C still passes \(0.707\) at the cutoff, so oversample rather than sitting exactly at \(2f_\text{cutoff}\).
4. What does clipping do beyond losing the peaks?
It creates new frequency content that was never in the original signal — so it corrupts the spectrum as well as the waveform.
5. What is dynamic range?
The span between a device's smallest and largest usable signal — for an ADC, \(V_\text{max} - V_\text{min}\). Conditioning exists to make the transducer's dynamic range and the converter's line up.
6. Why is wasted dynamic range a problem if nothing looks broken?
Because every unused level is resolution you paid for. A ±2 V signal into a ±5 V, 8-bit ADC uses only 40% of the range — 102 of 256 levels, about 6.7 effective bits out of the 8 you paid for.
7. Write the signal conditioning equation.
\(v_\text{out}(t) = K\,v_\text{in}(t) + B\) — gain \(K\) scales the span, bias \(B\) shifts the center.
8. How do you solve for K and B?
Map min to min and max to max. That gives two equations in two unknowns; subtract them to eliminate \(B\) and solve for \(K\), then back-substitute.
9. A transducer outputs −2 mV to +8 mV into an ADC spanning −5 V to +10 V. Find K.
Subtracting the endpoint equations: \(-15\ \text{V} = K(-10\ \text{mV})\), so \(K = 1500\). Then \(B = -2\ \text{V}\).
10. Must the gain K always be greater than 1?
No. If the transducer's span is larger than the ADC's, \(K < 1\) and the conditioning attenuates. Assuming conditioning always amplifies is a common error.
11. What is the last step of any conditioning calculation?
Check both endpoints in \(v_\text{out} = Kv_\text{in}+B\). It takes seconds and catches sign errors.