Hi everybody,

It's my first time posting here on AAC

I'm somewhat uncertain about my design for Exercise 1.24 from the Art of Electronics.

The exercise says the following:
Design a two-stage "bandpass" RC filter, in which the first stage is highpass with a breakpoint of 100Hz, and the second stage is lowpass with a breakpoint of 10kHz. Assume the input signal source has an impedance of 100 ohms. What is the worst-case output impedance of your filter, and therefore what is the minimum recommended load impedance?

I've attached a picture of the current design I have at the moment. I just focused on just creating a bandpass filter with the breakpoint frequency specs such that the bandpass was slightly wider than specified to make up for uncertainty in component tolerances.

What does it mean when they say to assume the input signal source has an impedance of 100 ohms? Is it just like how my design has a 100 ohm resistor attached in front of the input voltage?

Does the current design suffice or am I missing the point somewhere?

Also, how do I figure out the answers to the questions?

 

I'm somewhat uncertain about my design for Exercise 1.24 from the Art of Electronics.

Immediately preceding Exercise 1.24, AoE has the following instructions:

"So, for example, if you want to hang an RC lowpass filter onto the output of an amplifier whose output resistance is 100 Ω, start with R = 1k, then choose C for the breakpoint you want. Be sure that whatever loads the output has an input impedance of at least 10k. You can’t go wrong."

Did you start with R=1k, or did you go wrong?

 

Immediately preceding Exercise 1.24, AoE has the following instructions:

"So, for example, if you want to hang an RC lowpass filter onto the output of an amplifier whose output resistance is 100 Ω, start with R = 1k, then choose C for the breakpoint you want. Be sure that whatever loads the output has an input impedance of at least 10k. You can’t go wrong."

Did you start with R=1k, or did you go wrong?

I didn't follow those instructions because it said to put the lowpass filter as the second stage.

Was I supposed to follow those instructions after designing the highpass filter with an output resistance of 100 Ω?

 

I didn't follow those instructions because it said to put the lowpass filter as the second stage.

But in the previous section, AoE states: "D. Driving and loading RC filters … What we want to know, then, are the input and output impedances of the two simple RC filters (lowpass and highpass). … Now the answer is astonishingly simple: in all cases the worst-case impedance is just R."

I take that to mean that it does not matter whether the high-pass or low-pass is first.