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Am currently doing an assignment on sine wave generation and am using a sallen key band pass filter - i am unsure what the difference between the band pass filter and the sallen-key band pass.

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  • \$\begingroup\$ It's ok to ask questions about homework on stack exchange, but you need to show some effort to solve the problem before people will help you. You should google "types of bandpass filters", and then either add more detail to your question, or answer it yourself if you figure it out. \$\endgroup\$ – Drew Nov 1 '18 at 5:56
  • \$\begingroup\$ i had done research prior to posting this question, i still did not understand that there were "types" of bandpass filters, and that there was not just one main bandpass, that is why i asked the question. \$\endgroup\$ – user203022 Nov 1 '18 at 6:48
  • \$\begingroup\$ In my opinion, if you'd really done your research you would have read their TR-50 report in 1954. Not the published 1955 paper. But the one where you have to request that the US Air Force give you specific leave in order to get a copy. That, and the much smaller "digest" a year later would tell you more than enough for an answer. \$\endgroup\$ – jonk Nov 1 '18 at 9:17
  • \$\begingroup\$ @Cydney you need to show what you've got so far. Just saying "I tried" is not sufficient. \$\endgroup\$ – Drew Nov 1 '18 at 17:15
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There is no such thing as a "normal" bandpass filter - only different topologies. For instance alternative filters might be biquad or multiple feedback.

A Sallen-Key is widely used because (unlike the biquad, for instance) you can construct it using a single op-amp. The Sallen-Key is also useful because its design equations are simple.

If there is any bandpass which is "normal", in the sense of the most widely used, it's probably the Sallen-Key. A biquad has better sensitivity to component variations and the parameters gain, center frequency and Q are much more independent. That is, it's much easier to adjust a single variable than with a Sallen-Key. It also requires 3 or 4 op-amps to the Sallen-Key's one.

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    \$\begingroup\$ 30 years ago, "normal" would probably have meant a T or Pi passive filter. In some bands, it might still be the default choice. \$\endgroup\$ – The Photon Nov 1 '18 at 5:13
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There are lots of circuits that are band pass filters.

A Sallen-Key bandpass is just one of these circuits.

As compared to a passive filter, the Sallen-Key filter, like many active filter types, will be less affected by loading.

A Sallen-Key bandpass filter will be only a 1st-order filter (two poles, but generally the order of a bandpass filter is half the total number of poles).

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  • \$\begingroup\$ Regarding the order of a bandpass: There are two alternative definitions and - for my opinion - it is straight-forward (mostly used and and logical) to use the number of poles for defining the order. More than that, using the lowpass-bandpass transformation the number of poles is always doubled. Hence, a first order lowpass is transferred into a second order bandpass (lowest possible bandpass order). \$\endgroup\$ – LvW Nov 1 '18 at 10:12

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