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Frequency Division
I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave
to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. atb Mikw |
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Take a look at Analog Devices' line of DDS chips. Pretty much a one-chip
(needs ucontroller to drive it) digital solution to turn your 10MHz clock into virtually any frequency below 5 MHz (in theory; below 4MHz in easy practicality). The AD9834 only consumes 20mw at 3.3 VDC. There are many other devices in the product line. Many have built-in comparators to produce square-wave output. Joe W3JDR "Mike W" wrote in message ... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. atb Mikw |
Take a look at Analog Devices' line of DDS chips. Pretty much a one-chip
(needs ucontroller to drive it) digital solution to turn your 10MHz clock into virtually any frequency below 5 MHz (in theory; below 4MHz in easy practicality). The AD9834 only consumes 20mw at 3.3 VDC. There are many other devices in the product line. Many have built-in comparators to produce square-wave output. Joe W3JDR "Mike W" wrote in message ... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. atb Mikw |
"budgie" wrote in message ... On Wed, 18 Feb 2004 09:17:11 GMT, (Mike W) wrote: I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. Several approaches spring to mind. You stated "accurate" - they all provide that, but jitter is introduced in all of them: 1. VCO at 4MHz, divide by 4 and lock to Fref = 1MHz from your 10 Meg source divided by ten. 2. VCO at a multiple of 10M - say 40 MHz - locked to your 10M ref and divided down (by in this case 10) to give 4 MHz output. I would suggest using a 4MHz crystal oscillator as your VCO. Small varicap to alter the VXO frequency (or use an ordinary diode or LED as the varicap, see http://www.hanssummers.com/radio/varicap/varicap.htm). The inherent stability of the VXO will allow you to use a very slow PLL, which will result in minimal jitter. Hans G0UPL http://www.HansSummers.com |
"budgie" wrote in message ... On Wed, 18 Feb 2004 09:17:11 GMT, (Mike W) wrote: I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. Several approaches spring to mind. You stated "accurate" - they all provide that, but jitter is introduced in all of them: 1. VCO at 4MHz, divide by 4 and lock to Fref = 1MHz from your 10 Meg source divided by ten. 2. VCO at a multiple of 10M - say 40 MHz - locked to your 10M ref and divided down (by in this case 10) to give 4 MHz output. I would suggest using a 4MHz crystal oscillator as your VCO. Small varicap to alter the VXO frequency (or use an ordinary diode or LED as the varicap, see http://www.hanssummers.com/radio/varicap/varicap.htm). The inherent stability of the VXO will allow you to use a very slow PLL, which will result in minimal jitter. Hans G0UPL http://www.HansSummers.com |
Multiply by four, then divide by five and by two. Or divide by five,
then multiply by four and divide by two. For the best symmetry, you should expect to use a divide-by-two in the last stage, though you can get close to 50% with triggering off both rising and falling edges. There are other possible trick ways but the mpy/div are straightforward. You could, for example, divide the ref by five and a 4MHz VCO by two and build a PLL to control the 4MHz VCO. Cheers, Tom (Mike W) wrote in message ... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. atb Mikw |
Multiply by four, then divide by five and by two. Or divide by five,
then multiply by four and divide by two. For the best symmetry, you should expect to use a divide-by-two in the last stage, though you can get close to 50% with triggering off both rising and falling edges. There are other possible trick ways but the mpy/div are straightforward. You could, for example, divide the ref by five and a 4MHz VCO by two and build a PLL to control the 4MHz VCO. Cheers, Tom (Mike W) wrote in message ... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. atb Mikw |
In article ,
(Mike W) writes: I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. A more direct way, with very little jitter, is to double the 10 MHz reference with a dual diode arrangment, output tuned to 20 MHz, then into amplification (if needed), through a Schmitt inverter, another (!) dual diode doubler with output tuned to 40 MHz. Again amplification (if needed) and another Schmitt inverter to square up the 40 MHz. Divide the 40 MHz by 10 in a Johnson counter to achieve the 50% duty cycle. Broad tuning, no real problems there. Very direct. Minimal jitter. Johnson counters aren't common but they aren't made from unobtainium either. The CD4017 is an example and still available although it isn't fast enough for this application. Dividing by 10 via a Johnson counter needs a 5-stage shift register arrangement which can be done from 74LS or 74F or 74AC components (a 4-bit SR IC plus a flip-flop to complete the 5 stages). If operating at slower rates, the 50% duty cycle would appear at the "Carry Out" pin of a CD4017. A good simple explanation of Johnson counters is at: http://www.play-hookey.com/digital/johnson_counter.html Some other suggestions might suggest themselves if you explain the "timebase" in more detail. Len Anderson retired (from regular hours) electronic engineer person |
On Wed, 18 Feb 2004 13:07:48 -0000, "Hans Summers"
wrote: "budgie" wrote in message .. . On Wed, 18 Feb 2004 09:17:11 GMT, (Mike W) wrote: I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. Several approaches spring to mind. You stated "accurate" - they all provide that, but jitter is introduced in all of them: 1. VCO at 4MHz, divide by 4 and lock to Fref = 1MHz from your 10 Meg source divided by ten. 2. VCO at a multiple of 10M - say 40 MHz - locked to your 10M ref and divided down (by in this case 10) to give 4 MHz output. I would suggest using a 4MHz crystal oscillator as your VCO. Small varicap to alter the VXO frequency (or use an ordinary diode or LED as the varicap, see http://www.hanssummers.com/radio/varicap/varicap.htm). The inherent stability of the VXO will allow you to use a very slow PLL, which will result in minimal jitter. Agreed, a VCXO is a good way to go if you do need a VCO. Remember, the o/p didn't reference any jitter sensitivity in the task, which may be simple timing or gated counting of a pulse train. Neither is jitter-sensitive. If jitter isn't an issue, I'd personally KISS and go with #3. Small footprint, small dissipation, no tuned circuits, no PLL parameters to calculate, no VCO's to build, no VCXO's or xtals to buy. Only one RC time constant to calculate (or optimise by SOT) to minimise jitter if inclined to bother. |
On Wed, 18 Feb 2004 13:07:48 -0000, "Hans Summers"
wrote: "budgie" wrote in message .. . On Wed, 18 Feb 2004 09:17:11 GMT, (Mike W) wrote: I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. Several approaches spring to mind. You stated "accurate" - they all provide that, but jitter is introduced in all of them: 1. VCO at 4MHz, divide by 4 and lock to Fref = 1MHz from your 10 Meg source divided by ten. 2. VCO at a multiple of 10M - say 40 MHz - locked to your 10M ref and divided down (by in this case 10) to give 4 MHz output. I would suggest using a 4MHz crystal oscillator as your VCO. Small varicap to alter the VXO frequency (or use an ordinary diode or LED as the varicap, see http://www.hanssummers.com/radio/varicap/varicap.htm). The inherent stability of the VXO will allow you to use a very slow PLL, which will result in minimal jitter. Agreed, a VCXO is a good way to go if you do need a VCO. Remember, the o/p didn't reference any jitter sensitivity in the task, which may be simple timing or gated counting of a pulse train. Neither is jitter-sensitive. If jitter isn't an issue, I'd personally KISS and go with #3. Small footprint, small dissipation, no tuned circuits, no PLL parameters to calculate, no VCO's to build, no VCXO's or xtals to buy. Only one RC time constant to calculate (or optimise by SOT) to minimise jitter if inclined to bother. |
Thankyou everyone for your ideas.
I think I'll go with the VCXO phase locked to the 10Mhz reference. Why did'nt I think of that ;-( atb Mike W -- |
Thankyou everyone for your ideas.
I think I'll go with the VCXO phase locked to the 10Mhz reference. Why did'nt I think of that ;-( atb Mike W -- |
Do you need the accuracy of the frequency standard? Why not just buy a
little 4MHz CMOS crystal oscillator? If jitter and accuracy were important I'd either (hobby use) build a VXCO with an 8MHz crystal referenced to 2MHz from the standard or (for a customer design) buy an integrated 4MHz VXCO and reference it to 2MHz from the standard. In either case I'd use the phase comparator from a 74HC4046 or an exclusive OR gate. You'll be using a divide-by 5 which can be had from a 74HC390 if they're still available, and a divide-by 2 or 4, which can be had from just about anything -- including the same 74HC390 if your hookup is a little perverse. All the logic _could_ be done on a PAL, of course. Come to think of it if absolute accuracy is important but jitter isn't you can just use the oscillator from the '4046 as well, with the same division scheme. -------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com "Mike W" wrote in message ... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. atb Mikw |
Do you need the accuracy of the frequency standard? Why not just buy a
little 4MHz CMOS crystal oscillator? If jitter and accuracy were important I'd either (hobby use) build a VXCO with an 8MHz crystal referenced to 2MHz from the standard or (for a customer design) buy an integrated 4MHz VXCO and reference it to 2MHz from the standard. In either case I'd use the phase comparator from a 74HC4046 or an exclusive OR gate. You'll be using a divide-by 5 which can be had from a 74HC390 if they're still available, and a divide-by 2 or 4, which can be had from just about anything -- including the same 74HC390 if your hookup is a little perverse. All the logic _could_ be done on a PAL, of course. Come to think of it if absolute accuracy is important but jitter isn't you can just use the oscillator from the '4046 as well, with the same division scheme. -------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com "Mike W" wrote in message ... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. atb Mikw |
"Mike W" wrote in message
... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. I'd be tempted to use a PAL chip. It is possible to make a multiply by 4 and then divide by 10 in the same chip, which would make the total parts required to get the 4 MHz 50% Sq Wave your original 10 MHz input and a single chip. Jim Pennell N6BIU |
"Mike W" wrote in message
... I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave to use as a timebase. I have a 10Mhz IQD frequency standard of suitable accuracy. How can I divide this to produce the 50% duty cycle 4Mhz signal?. Is it even possible with logic alone?. I can see how to mix with either 6Mhz or 14Mhz, but this then detracts from the required accuracy. I'd be tempted to use a PAL chip. It is possible to make a multiply by 4 and then divide by 10 in the same chip, which would make the total parts required to get the 4 MHz 50% Sq Wave your original 10 MHz input and a single chip. Jim Pennell N6BIU |
On Fri, 20 Feb 2004 03:08:14 GMT, "Jim Pennell"
wrote: I'd be tempted to use a PAL chip. It is possible to make a multiply by 4 and then divide by 10 in the same chip, which would make the total parts required to get the 4 MHz 50% Sq Wave your original 10 MHz input and a single chip. Mice one Jim. 1. buy your PAL programmer 2. buy your PAL 3. learn how to obtain the required function 4. burn the PAL and discover it does'nt work 5. while patience lasts go to 2. wend 6. revert to PLL |
On Fri, 20 Feb 2004 03:08:14 GMT, "Jim Pennell"
wrote: I'd be tempted to use a PAL chip. It is possible to make a multiply by 4 and then divide by 10 in the same chip, which would make the total parts required to get the 4 MHz 50% Sq Wave your original 10 MHz input and a single chip. Mice one Jim. 1. buy your PAL programmer 2. buy your PAL 3. learn how to obtain the required function 4. burn the PAL and discover it does'nt work 5. while patience lasts go to 2. wend 6. revert to PLL |
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Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? -- The BBC: Licensed at public expense to spread lies. |
Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? -- The BBC: Licensed at public expense to spread lies. |
Paul Burridge wrote in message ... Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? -- The BBC: Licensed at public expense to spread lies. LM1496 |
Paul Burridge wrote in message ... Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? -- The BBC: Licensed at public expense to spread lies. LM1496 |
On Sat, 21 Feb 2004 12:28:13 +0000, Paul Burridge
wrote: Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? give 'em a call for free samples... EUROPE Hittite Microwave Europe Ltd Sales and Applications 4.1 Intec Wade Road, Basingstoke Hampshire, RG24 8NE, United Kingdom E-Mail: Phone: +44 1-256-817-000 Fax: +44 1-256-817-111 [] Remove "HeadFromButt", before replying by email. |
On Sat, 21 Feb 2004 12:28:13 +0000, Paul Burridge
wrote: Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? give 'em a call for free samples... EUROPE Hittite Microwave Europe Ltd Sales and Applications 4.1 Intec Wade Road, Basingstoke Hampshire, RG24 8NE, United Kingdom E-Mail: Phone: +44 1-256-817-000 Fax: +44 1-256-817-111 [] Remove "HeadFromButt", before replying by email. |
Paul Burridge wrote: Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? What sort of performance is required? Diode mixers are easy to obtain and have good IMD characteristics. The impedances on the ports need to be properly matched. Leon -- Leon Heller, G1HSM Email: My low-cost Philips LPC210x ARM development system: http://www.geocities.com/leon_heller/lpc2104.html |
Paul Burridge wrote: Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? What sort of performance is required? Diode mixers are easy to obtain and have good IMD characteristics. The impedances on the ports need to be properly matched. Leon -- Leon Heller, G1HSM Email: My low-cost Philips LPC210x ARM development system: http://www.geocities.com/leon_heller/lpc2104.html |
On Sat, 21 Feb 2004 18:22:44 +0000, Leon Heller
wrote: Paul Burridge wrote: Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? What sort of performance is required? "Good." :-) Diode mixers are easy to obtain and have good IMD characteristics. The impedances on the ports need to be properly matched. What - the sort of crossed diode config one often sees in the ham design books? Do you think I might as well just make one up from discretes? I'm basically just trying to combine 60Mhz with 20Mhz to end up with the difference frequency in this case. JJ suggested a chip, but looking at the data sheet, it seemed to be designed more as a modulator than a mixer. Let's not get into an argument over semantics but y'all know what I mean, I'm sure. BTW, thanks for a good steer with the Pulsonix suggestion, Leon. I'm making good progress getting to grips with it. -- The BBC: Licensed at public expense to spread lies. |
On Sat, 21 Feb 2004 18:22:44 +0000, Leon Heller
wrote: Paul Burridge wrote: Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? What sort of performance is required? "Good." :-) Diode mixers are easy to obtain and have good IMD characteristics. The impedances on the ports need to be properly matched. What - the sort of crossed diode config one often sees in the ham design books? Do you think I might as well just make one up from discretes? I'm basically just trying to combine 60Mhz with 20Mhz to end up with the difference frequency in this case. JJ suggested a chip, but looking at the data sheet, it seemed to be designed more as a modulator than a mixer. Let's not get into an argument over semantics but y'all know what I mean, I'm sure. BTW, thanks for a good steer with the Pulsonix suggestion, Leon. I'm making good progress getting to grips with it. -- The BBC: Licensed at public expense to spread lies. |
Anyone care to nominate an RF mixer chip for 100Mhz that's readily
available in the UK? ================================ SA602AN as well as SA612AN each costing GBP 2.50 Both have on-board LO circuit. www.modecomponents.co.uk ,probably also from www.jabdog.com Both companies are in the Birmingham area. If you are a member of G-QRP Club the SA602AN is somewhat cheaper from Club Sales. Frank GM0CSZ / KN6WH |
Anyone care to nominate an RF mixer chip for 100Mhz that's readily
available in the UK? ================================ SA602AN as well as SA612AN each costing GBP 2.50 Both have on-board LO circuit. www.modecomponents.co.uk ,probably also from www.jabdog.com Both companies are in the Birmingham area. If you are a member of G-QRP Club the SA602AN is somewhat cheaper from Club Sales. Frank GM0CSZ / KN6WH |
The Philips SA602 or SA612 ought to be available in the UK. Don't overload
the RF port though, the gain folds back over 200mV RF input -- confuses the hell out of an AGC loop. "Paul Burridge" wrote in message ... Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? -- The BBC: Licensed at public expense to spread lies. |
The Philips SA602 or SA612 ought to be available in the UK. Don't overload
the RF port though, the gain folds back over 200mV RF input -- confuses the hell out of an AGC loop. "Paul Burridge" wrote in message ... Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? -- The BBC: Licensed at public expense to spread lies. |
On a sunny day (Sat, 21 Feb 2004 19:22:15 +0000) it happened Paul Burridge
wrote in : On Sat, 21 Feb 2004 18:22:44 +0000, Leon Heller wrote: Paul Burridge wrote: Anyone care to nominate an RF mixer chip for 100Mhz that's readily available in the UK? What sort of performance is required? "Good." :-) Diode mixers are easy to obtain and have good IMD characteristics. The impedances on the ports need to be properly matched. What - the sort of crossed diode config one often sees in the ham design books? Do you think I might as well just make one up from discretes? I'm basically just trying to combine 60Mhz with 20Mhz to end up with the difference frequency in this case. JJ suggested a chip, but looking at the data sheet, it seemed to be designed more as a modulator than a mixer. Let's not get into an argument over semantics but y'all know what I mean, I'm sure. BTW, thanks for a good steer with the Pulsonix suggestion, Leon. I'm making good progress getting to grips with it. I do this with a dual gate MOSFET, osc on second gate, signal on first. A voltage divider on gate 2 to set it in teh non-linear part. This works very well, is not critical, very cheap and extremely reliable. Also the noise figure is good. So tuned 40MHz in drain I did one some weeks agao, but cant remember what that was for? Anyway that sceme works up to a GHz , from kHz up. If you need diagram and part example I could draw up one here. Copyright Jan Panteltje 2004 All Right Reserved By reading this you agree to pay me 1 fc. |
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