I wanted to create RC lowpass filter with cutoff frequency 15 kHz and output impedance 50 ohm. What should be R and C values? I'm a little confused how to interpret 50 ohm output impedance to calculate values. I figured it out, it should be R = 35 ohm and C = 300 nF.
The output driving RC filter is the output of LMC6001 amplifier, which has 0.07 ohm.
It would be best if I could get the output impedance 50 ohm for frequencies from DC to 15 kHz.
Thank you for your explanation.
Edit Just noticed the question specifies that the output impedance should be 50 Ω up to the filter cutoff. In that case, just choose \$R = 50 Ω\$ and \$C = 1/(2 \pi \cdot 50 \Omega \cdot 15 kHz)\$.
If you analyze the output impedance of a simple RC filter (shown below), you will see that it is a function of frequency. Your specification of 50 Ω can only be met at a specific frequency. Otherwise, you need to use a different circuit.
For a broadband output impedance of 50 Ω, Andy's suggestion in the comments to use a buffer is probably the simplest. It preserves the transfer function of the filter but modifies the output impedance.
An alternative, but questionably practical, circuit is shown below. It has the same transfer function as the simple RC filter, but it maintains a constant output impedance equal to the value of the resistors. The value of the capacitor and inductor must obey \$L/C = R^2\$.
