clueless84 Posted April 11, 2005 Report Share Posted April 11, 2005 Hi All, I'm currently doing a project for college, Design of Switched capacitor filtersfor a PCM Speech CODEC. I am to use a biphase clock to drive the switches on the capacitor. This is where my problems begin. I do not know how to design a biphase clock, I was told to use a johnson counter, but when I implemented this it just gave me 2 signals in phase. Any help would be appreciated. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 11, 2005 Report Share Posted April 11, 2005 Hi Clueless, Welcome to our forum.Aren't you allowed to use a switched-capacitor filter IC? Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted April 11, 2005 Report Share Posted April 11, 2005 What's this, problems with the clock. You shift your phase back upstream where you have the sine wave oscillator. A series RC will give you the phase difference. Then the sine wave oscillator is converted to a square wave. This is the method of choice anyhow. Quote Link to comment Share on other sites More sharing options...
clueless84 Posted April 12, 2005 Author Report Share Posted April 12, 2005 No we have to built everything, well I think we can buy certain parts if we're really stuck, not sure though. How do you shift the phase back upstream? As the name would suggest, I really am quite clueless. Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 12, 2005 Report Share Posted April 12, 2005 Hi Clueless,Switched capacitor filter ICs use a "non-overlapping clock generator". I don't know how to make one easily using a Johnson Counter like a CD4018, maybe it needs two cascaded CD4018 counters. Please post your Johnson Counter defective bi-phase clock circuit so we can troubleshoot it. Quote Link to comment Share on other sites More sharing options...
clueless84 Posted April 12, 2005 Author Report Share Posted April 12, 2005 I'm using a 2 D type flip flop's. I dunno if my diagram will appear, hopefully it will, i'm new to all this. The chip i'm using is a 74LS74, i'm using a 10K square wave pulse. If my diagram posts, I was originally using the output C1 from between Q1 and D2. I have now changed it bit I think my power supply has decided to act up so i'll get back to you when I figure it out. Quote Link to comment Share on other sites More sharing options...
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