100Hz(required)-500kHz(uaximum) varying oscillator - Electronic Circuits Projects Diagrams Free

dknguyen · 7th May 2006, 10:23 AM

I need to control the cutoff frequency for several LP filters independently. Their cutoff frequency 1/100th of the input clock frequency. I need to try and find an oscillator/clock generator (preferably multiple clock signals in a single IC) that can go 100Hz and up (with max of 500kHz, but this maximum can be much MUCH MUCH MUCH lower). It needs to be programmable without external resistors or capacitors (I need the MCU to be able to control the frequency).

Anyone know of such a software-programmable low-frequency multiple-clock generator?

Papabravo · 7th May 2006, 05:09 PM

There are probably as many options as there are cross ties on the railroad tracks. The microprocessor itself is a candidate for producing a variable clock output. That output can feed a bank of flip-flops or counters which will provide outputs until the cows come home. There are also numerous serially programmable frequency synthesizers that cover DC to blue light.

The challenge is not in the minimum or maximum frequency but in the step size or granularity of the frequencies you want to produce.

dknguyen · 7th May 2006, 07:54 PM

Can a 50% PWM pulse be used as a clock?

**Nigel Goodwin** · 7th May 2006, 07:56 PM

Quote:

Originally Posted by dknguyen

Can a 50% PWM pulse be used as a clock?

Yes, but it seems rather a waste?.

dknguyen · 7th May 2006, 08:14 PM

Why does it seem like a waste? TO me it seems like the ultimate in flexibility...although you are wasting an MCU if that's what you are referring to.

Papabravo · 8th May 2006, 02:28 AM

Yes but using the PWM output can really limit your choice of frequency. I think it is better to create your own output based on loading a timer to a sepcific value with an auto reload and an output toggle.

**Nigel Goodwin** · 8th May 2006, 09:12 AM

Quote:

Originally Posted by dknguyen

Why does it seem like a waste? TO me it seems like the ultimate in flexibility...although you are wasting an MCU if that's what you are referring to.

In that you're wasting a useful piece of hardware, by using it for a purpose it's not very good for - far easier, and far more useful, to simply generate it in software. PWM modules are intended for a specific purpose, and they are excellent for that, but rather limited for other uses.

dknguyen · 8th May 2006, 06:02 PM

Oh, that's what I meant. Using PWM generated in software by an MCU. I have also noticed that PWM modules have a small range of frequencies.

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7th May 2006, 10:23 AM	(permalink)
dknguyen	100Hz(required)-500kHz(uaximum) varying oscillator I need to control the cutoff frequency for several LP filters independently. Their cutoff frequency 1/100th of the input clock frequency. I need to try and find an oscillator/clock generator (preferably multiple clock signals in a single IC) that can go 100Hz and up (with max of 500kHz, but this maximum can be much MUCH MUCH MUCH lower). It needs to be programmable without external resistors or capacitors (I need the MCU to be able to control the frequency). Anyone know of such a software-programmable low-frequency multiple-clock generator?

7th May 2006, 05:09 PM	(permalink)
Papabravo	There are probably as many options as there are cross ties on the railroad tracks. The microprocessor itself is a candidate for producing a variable clock output. That output can feed a bank of flip-flops or counters which will provide outputs until the cows come home. There are also numerous serially programmable frequency synthesizers that cover DC to blue light. The challenge is not in the minimum or maximum frequency but in the step size or granularity of the frequencies you want to produce.

7th May 2006, 07:54 PM	(permalink)
dknguyen	Can a 50% PWM pulse be used as a clock?

7th May 2006, 08:14 PM	(permalink)
dknguyen	Why does it seem like a waste? TO me it seems like the ultimate in flexibility...although you are wasting an MCU if that's what you are referring to.

8th May 2006, 02:28 AM	(permalink)
Papabravo	Yes but using the PWM output can really limit your choice of frequency. I think it is better to create your own output based on loading a timer to a sepcific value with an auto reload and an output toggle.

8th May 2006, 06:02 PM	(permalink)
dknguyen	Oh, that's what I meant. Using PWM generated in software by an MCU. I have also noticed that PWM modules have a small range of frequencies.