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| Aol = 22 for a single stage, so ignoring loading effects Aol
= 22 * 22 * 22 = 10,000 approx.
Acl = (Rf/Ri+Rf) * (Aol/(1+BAol) where B = Ri/(Rf+Ri) = 0.01/10.01 = 0.001 to three significant figures whence Acl = (10/10.01)*(10,000/(1+10,000*0.001)) = 0.9990 * 909 = 908 |
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| By experiment we find Acl = 920 at input frequency Fin of 1kHz and Acl = 640 at Fin = 100kHz. | |
| The three stage amplifier is suitable both in terms of
available gain and bandwidth (140kHz) as an input preamp for our
detector. Apart from the IC it uses only four components. (Not
shown: supply decoupling C 0.01uF) Note that as the input is AC coupled via C1 the circuit is self-biasing into its optimum DC condition. |
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| An alternative design used three separate stages each designed for a gain of ten and then cascaded. The circuit used lots more components and no benefit was noted, so we use the simpler circuit. |