# what's the difference between these two low pass filter types

Is there any difference between these two types of lowpass filters? I see the equation is the same, I assume they're both first order then. Just curious if there's any practical difference. Maybe one allows me to set gain and the other doesn't?

• For one, the top one is inverting and the bottom is non-inverting. – Null Nov 12 '14 at 2:11
• Also, the top one can have passband gain, while the lower one has gain of 1. – The Photon Nov 12 '14 at 2:19
• @confused, you might be interested in this book from TI: PLL Performance, Simulation, and Design Handbook – The Photon Nov 12 '14 at 2:22
• @ThePhoton I take it that the second comment was meant for confused's other question about PLL's? – helloworld922 Nov 12 '14 at 2:59
• @helloworld922, I'm assuming this question is also about PLLs (specifically, about the loop filter). – The Photon Nov 12 '14 at 3:36

$$H(s)=\frac{-R_{2}}{R_{1}} \times \frac{1}{1+R_{2}C_{2}s}$$
$$H(s)=\frac{1}{RCs+1}$$