lab4_freq_resp_notes

lab4_freq_resp_notes - ECE 209 Circuits and Electronics...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ECE 209: Circuits and Electronics Laboratory Notes for Lab 4 (Frequency Response of First-Order Active Circuits) 1. Comments on returned lab report. • Put units on tables and figures and show individual data points (i.e., not just interpolation). • In meters lab, positive error on R v is a good thing. Manufacturer gives worst-case specification. 2. First-order active filters. • Active filters allow for gain, simplicity, robustness, and can have hard “knees” without inductors. • Use standard inverting/non-inverting OA configuration, but use (equivalent) Laplace-domain impedances instead of simple resistances. • To quickly determine characteristic of filter (i.e., low-pass, high-pass, or bandpass) consider what happens to OA configuration’s “gain” at some sample frequencies. – In today’s lab, both filter’s have transfer function given by − Z F ( s ) /Z I ( s ). – In the low-pass filter, Z I ( s ) = R 1 and Z F ( s ) = R 2 bardbl ( sC ) − 1 . * Z F (0) ≈ R 2 for low frequencies — LF gain is − R 2 /R 1 (i.e., R 2 /R 1 with − 180 ◦ shift). * Z I ( jω ) ≈ 0 for high frequencies — HF gain is − /R 1 ≈ 0 (with − 180 ◦ − 90 ◦ shift). * First-order filter’s time constant τ must depend on C , but because V − is a virtual ground, the output does not “feel” the effect of R 1 . So time constant τ = R 2 C . * It is a low-pass filter with passband gain K = − R 2 /R 1 and time constant τ = R 2 C : H LPF ( s ) defines K τs + 1 = − R 2 R 1 sR 2 C + 1 . – In the high-pass filter, Z I ( s ) = R 1 + 1 / ( sC ) and Z F ( s ) = R 2 . * Z I (0) ≈ ∞ (i.e., “open” for VLF) — LF gain is − R 2 / ∞ ≈ 0 (with − 180 ◦ + 90 ◦ shift). * Z I ( jω ) ≈ R 1 for high frequencies — HF gain is − R 2 /R 1 (i.e., R 2 /R 1 with − 180 ◦ shift). * First-order filter’s time constant τ must depend on C , but because V − is a virtual ground, the input does not “feel” the effect of R 2 . So time constant τ = R 1 C ....
View Full Document

{[ snackBarMessage ]}

Page1 / 3

lab4_freq_resp_notes - ECE 209 Circuits and Electronics...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online