Post by thread:clock multiplier for switched cap filter ?

Hi, I'm trying to build a programmable bandpass filter whose center frequency is controlled by a PIC16C84. I need to filter audio signals between about 200Hz up to 1500Hz under software control. I was hoping to be able to use a switched capacitor filter, e.g. National Semiconductor MF-8 or the equivalent Linear Tech Part. For these devices you control the center frequency via an external clock signal running at either 50x or 100x of the desired center frequency (which I had hoped the PIC could provide). The PROBLEM is that 1500 Hz * 100 = 150000 which is too fast for a 4 or 10 or 20 MHz clocked PIC to do, I think. I've tried various types of codes from the EASY PIC'N book and from frequency generation ideas using phase accumulators by Scott Dattalo within the MPSIM simulator and I can only get a clock to go at about 22 kHz using any of these methods -- not nearly fast enough. The phase accumulator method is preferred, since the application is musical note identification and the frequencies are oddball multiples of the PIC clock frequency. THEREFORE -- If I'm going to continue on this tack, I need a clock multiplier to hang on the output of the PIC to boost up the frequency a bunch (several clock doublers ??). Any good ideas here? By the way I did run across a programmable sine wave generator chip good from DC to 500 kHz from MicroLinear -- I suppose this could be squared up and used as a clock. the problem is that I can't seem to find small quantities for sale, they want to sell tubes of 25 for $10.00 each. Any help or suggestions are greatly appreciated. Steve -- +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Stephen Brown, Ph.D. Applied Research Associates RR 1 Box 120A, Waterman Road South Royalton, Vermont 05068 (802) 763-8348 voice (802) 763-8283 fax spam_OUTsbrownTakeThisOuTned.ara.com +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

> Hi, > had hoped the PIC could provide). The PROBLEM is that 1500 Hz * 100 = > 150000 which is too fast for a 4 or 10 or 20 MHz clocked PIC to do, I > THEREFORE -- If I'm going to continue on this tack, I need a clock > multiplier to hang on the output of the PIC to boost up the frequency > a bunch (several clock doublers ??). Any good ideas here? > Try a 4046 or 74hc4046. They are cheap and relatively easy to use ( for a phase locked loop). These are made by Motorola, Harris, National,and I'm sure others & operate in the frequency range you need. Look at Motorola AN535 for a primer on phase locked loop design. The data sheets for the parts also give some basic equations that will get the part working. --------------------------------------------------------------------- Jonathan King | .....kingKILLspam@spam@uicc.com Unitrode Corp. | http://www.unitrode.com 7 Continental Blvd | (603) 429-8715 Merrimack, NH 03054 | (603) 424-3460

At 08:49 AM 4/15/97 -0400, you wrote: >THEREFORE -- If I'm going to continue on this tack, I need a clock >multiplier to hang on the output of the PIC to boost up the frequency >a bunch (several clock doublers ??). Any good ideas here? > Hi Steve, Why don't you change your design and use another way to generate clock for the switched cap filter? You can use Motorola MC145162 universal dual PLL, you only use this chip to divide crystal clock(5MHz or others) into the switch cap filter clock, for a 150000Hz clock, use 5MHZ/33=150KHz. since the MC145162 is a dual PLL, so you can use it to generate two different clock for different filter frequencies :) The price for MC145162 is about 1.5 US$ each for QTY 25. It is SPI compatible, friendly to PIC. More info, you can check the Motorola web, there is a PDF data sheet upon MC145162. Jerry Meng, BA1FB ba1fbKILLspamqsl.net .....ba1fbKILLspam.....amsat.org http://www.qsl.net/ba1fb

|>By the way I did run across a programmable sine wave generator chip |>good from DC to 500 kHz from MicroLinear -- I suppose this could be |>squared up and used as a clock. |Why don't you try a programmable divider (from 20MHz)? It probably gives |you enough resolution. [nb: Does anyone know a good way to make MS Exchange format replies properly without having to hand-insert all the "|" or ">" characters?] A "conventional" clock divider running from 20MHz won't have much resolution around 500KHz. Your steps would be: 487,805Hz 500,000Hz 512,821Hz etc. [i.e. about 12KHz resolution]. You may get much finer resolution if you don't mind a little bit of "jitter" in the output. You may get any frequency you want, to arbitrary accuracy, with 1/2 clock-period of jitter by building a suit- able-length accumulator (i.e. adders and latches). If you build, say, a 16-bit accumulator and put 2193 on the input, then the MSB of the output will toggle at a speed (2193/65536) times the cycle rate. Alternatively, if you don't mind having a bit more jitter, you may use a simpler technique as found in a 4089 [a cute but not terribly useful part which has been discontinued; if you can find the data sheet for it somewhere, though, you'll see what I'm talking about]. A 22v10 fed with a 20MHz clock should be able to produce any frequency from 39,139Hz to 10,000,000Hz within 0.4% [if you were to use this route, you'd need 11 out- puts from the PIC to set the desired output speed but the PIC itself wouldn't have to do anything]. If more accuracy is need- ed, you could change the circuit a little bit and have the PIC "fine-tune" the output (the circuit itself works as a divide-down counter that selectively "drops" counts; the PIC could "drop" a few more if needed). This technique, by the way, works best when the output frequency is much below the input frequency, or when it will be divided down so jitter doesn't matter too much (the device works by producing a frequency between 1/2 and 1/4 of the input frequency and then dividing that by a power of two; the more stages you divide it the less jitter will remain). If you use it for audio, you need to divide it by at least 100 in order to eliminate the jitter comp- onents. For your applications, though, it sounds as though that shouldn't be too much of a problem.

At 06:45 PM 4/15/97 -0500, you wrote: {Quote hidden}>|>By the way I did run across a programmable sine wave generator chip >|>good from DC to 500 kHz from MicroLinear -- I suppose this could be >|>squared up and used as a clock. > >|Why don't you try a programmable divider (from 20MHz)? It probably gives >|you enough resolution. > >[nb: Does anyone know a good way to make MS Exchange format >replies properly without having to hand-insert all the "|" or >">" characters?] > >A "conventional" clock divider running from 20MHz won't have much >resolution around 500KHz. Your steps would be: > > 487,805Hz > 500,000Hz > 512,821Hz > >etc. [i.e. about 12KHz resolution]. You may get much finer >resolution if you don't mind a little bit of "jitter" in the >output. You may get any frequency you want, to arbitrary >accuracy, with 1/2 clock-period of jitter by building a suit- >able-length accumulator (i.e. adders and latches). If you >build, say, a 16-bit accumulator and put 2193 on the input, >then the MSB of the output will toggle at a speed (2193/65536) >times the cycle rate. > >Alternatively, if you don't mind having a bit more jitter, you >may use a simpler technique as found in a 4089 [a cute but not >terribly useful part which has been discontinued; if you can >find the data sheet for it somewhere, though, you'll see what >I'm talking about]. A 22v10 fed with a 20MHz clock should be >able to produce any frequency from 39,139Hz to 10,000,000Hz >within 0.4% [if you were to use this route, you'd need 11 out- >puts from the PIC to set the desired output speed but the PIC >itself wouldn't have to do anything]. If more accuracy is need- >ed, you could change the circuit a little bit and have the PIC >"fine-tune" the output (the circuit itself works as a divide-down >counter that selectively "drops" counts; the PIC could "drop" a >few more if needed). > >This technique, by the way, works best when the output frequency >is much below the input frequency, or when it will be divided down >so jitter doesn't matter too much (the device works by producing >a frequency between 1/2 and 1/4 of the input frequency and then >dividing that by a power of two; the more stages you divide it the >less jitter will remain). If you use it for audio, you need to >divide it by at least 100 in order to eliminate the jitter comp- >onents. For your applications, though, it sounds as though that >shouldn't be too much of a problem. > > Hi John, If you need a fine resolution high speed clock source, why don't you try the new technology Direct Digital Synthesizer, Like AD9850, it can generate up to 42MHz with a 125MHz clock input , output tuning resolution of 0.0291 Hz. The AD9850 also contains a high speed comparator which can be configured to accept the (externally) filtered output of the DAC to generate a low jitter square wave output. But the cost is much higher. Jerry Meng, BA1FB EraseMEba1fbspam_OUTTakeThisOuTqsl.net ba1fbspam_OUTamsat.org http://www.qsl.net/ba1fb

In message <@spam@199704151249.IAA01745KILLspamterrier.ned.ara.com> KILLspamPICLISTKILLspamMITVMA.MIT.EDU writes: Hi, > I'm trying to build a programmable bandpass filter whose center > frequency is controlled by a PIC16C84. I need to filter audio signals > between about 200Hz up to 1500Hz under software control. I was hoping > to be able to use a switched capacitor filter, e.g. National > Semiconductor MF-8 or the equivalent Linear Tech Part. [snipped] You don't explain exactly what you are trying to do, but in the current issue (May 97) of 'Everyday Practical Electronics' they have a project for a 'Musical Instrument Tuner' using a 10MHz 16C84. It picks up the audio via a microphone and (optionally) bandpass filters it using an LM13600 controlled by an D2A fed from PORT B, after calculation the nearest note and percentage error is displayed on an LCD module. The software can be downloaded from their web site, http://www.epemag.wimborne.co.uk Nigel. /--------------------------------------------------------------\ | Nigel Goodwin | Internet : RemoveMEnigelgTakeThisOuTlpilsley.demon.co.uk | | Lower Pilsley | Web Page : http://www.lpilsley.demon.co.uk | | Chesterfield | | | England | | \--------------------------------------------------------------/

On Tue, 15 Apr 1997, Jonathan King wrote: > Try a 4046 or 74hc4046. They are cheap and relatively easy to use ( for a > phase locked loop). These are made by Motorola, Harris, National,and I'm sure > > Look at Motorola AN535 for a primer on phase locked loop design. The data hello, is this application note available on the net. if yes could you give the web site address ??? thanx, vishram. Character Density, n.: The number of very weird people in the office. +------------------------------------------+ | Vishram A. Sarurkar | | ^^^^^^^^^^^^^^^^^^^^^ | | another hobbyist turned researcher | | slogging @ Indian Institute of Science | | ----------- | | e-mail:spamBeGonevishspamBeGoneisu.iisc.ernet.in. | | Phone:+91 (080) 3092487. | +------------------------------------------+