question : tuning for active RC filter corner frequency

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linuxwinner

Joined: 25 Nov 2005
Posts: 13

25 Aug 2009 5:54 corner frequency

Hi folks,

There is active RC filter with frequency tuning circuit. The tuning circuit results indicate that the RC time constant tends to be large. But the bandwidth of the filter tends to be wide. Is there any factor introducing the discrepancy? Thanks!

LvW

Joined: 07 May 2008
Posts: 1466
Helped: 242
Location: Germany

25 Aug 2009 8:39 tuning

I like to answer you - however, I don´t understand your question, sorry.

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linuxwinner

Joined: 25 Nov 2005
Posts: 13

25 Aug 2009 8:48 rc frequency chart for germany

Thanks for your intention! The situation is that RC variation can vary the corner frequency of active RC filter. For keeping track of the RC variation, tuning circuit is used.

LvW

Joined: 07 May 2008
Posts: 1466
Helped: 242
Location: Germany

25 Aug 2009 9:24 rc filter

linuxwinner wrote:

Thanks for your intention! The situation is that RC variation can vary the corner frequency of active RC filter. For keeping track of the RC variation, tuning circuit is used.

Yes, but what is your problem now ?

linuxwinner

Joined: 25 Nov 2005
Posts: 13

25 Aug 2009 9:31 rc circuit corner frequency

The problem is that:

Tuning circuit detects that master RC time constant is large. Large RC time constant means that the slave RC in active RC filter should be also large such that bandwidth of the filter should be narrow. But actually, the bandwidth of the filter is wider than expected. How come there is discrepancy?

tzg6sa

Joined: 03 Jun 2008
Posts: 12
Location: Hungary

25 Aug 2009 11:33 calculate rc corner frequency

It would help a lot if you would show us a drawing from the circuit.

LvW

Joined: 07 May 2008
Posts: 1466
Helped: 242
Location: Germany

25 Aug 2009 11:40 active rc filter

tzg6sa wrote:

It would help a lot if you would show us a drawing from the circuit.

Yes, I agree. How could we know without any drawing?

rfsystem

Joined: 25 Feb 2002
Posts: 858
Helped: 96

26 Aug 2009 23:26 rc filter circuit

As I understand is that the reference circuit indicating that 1/RC is lower than your reference clock frequency. But the change on the filter circuit is that the bandwidth is set to higher frequencies.

This is correct!

If you verify both, the reference tuner and the filter and apply the same process/temperature depend RC, the filter sould be with the tolerance or resolution of the setting method.