time constant of integrator

Discussion in 'The Projects Forum' started by albertino, Nov 3, 2009.

1. albertino Thread Starter New Member

Apr 9, 2008
5
0
Good afternoon to everyone,
I have got a quick question for you guys.
I'm going to build a delta modulator for my final year project.
The signal into the modulator will be a sine wave of 3khz (to simulate human voice) and after passing through a comparator and a d type flip flop, it will be reconstructed by an integrator (basically it's an active low pass filter with a resistor into the negative input, a capacitor and a resistor in parallel on the negative feedback loop and two identical resistors to form a voltage divider rule connected to the positive input ( i'm looking to another circuit and considering that the op amp will operate with one supply, i think this is done because I will be working half way between +Vcc and ground).

I have seen on some projects on the internet that a time constant of 1ms will be enough to reconstruct my signal.

My questions are:

Is the time constant the product of the resistor and capacitor in parallel on the negative feedback loop? Do i have to include even the single resistor on the negative input? If yes, why???

Why, for a range of frequency between 300 Hz and 3Khz, a time constant of 1 ms is enough to reconstruct the signal?? What is the right way of reasoning and decide the right time constant knowing the maximum frequency of the system to be reconstructed???