Electronics Made Easy by Martin Denny;James Denny

Author:Martin Denny;James Denny
Language: eng
Format: mobi
Publisher: Pixeko LLP
Published: 2009-06-30T23:00:00+00:00

Figure 6 shows a square waveform with uneven Mark-Space Ratio. The mark-space ratio = T1:T2 and the pulse repetition frequency f = 1/(T1+T2).

ACTIVE FILTERS

Filters are defined as either high pass (HPF, passing high frequency signals), low pass (LPF, blocking high frequency signals), or notch which contains elements of both high and low pass, and can either pass or exclude signals within a narrow band of frequencies.

Figure 7 shows a conventional low pass filter network, combined with a non-inverting amplifier with a gain of 4.3* or 12.db see below:

G = (R4 + R3)/R3 = (33K + 10K)/10K = 4.3

To convert Gain to decibels: G = 20 Log 4.3 = 12.6db

An Approximation of Fc is calculated as follows:

Fc = 1/(2pRC) = 10^6/2*3.142*33*10^3 * 0.01 = 482Hz

Where: R = R1 = R2 and C = C1 = C2. and Fc is the cut off frequency and is defined as the frequency when the gain falls by 3db (-3db point).

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