On Fri, 30 Apr 2021 19:18:10 +0100, Piglet <erichpwagner@hotmail.com> wrote:>On 30/04/2021 16:45, jlarkin@highlandsniptechnology.com wrote: >> On Fri, 30 Apr 2021 08:07:10 +0300, upsidedown@downunder.com wrote: >> >>> On Tue, 27 Apr 2021 12:35:17 -0700, John Larkin >>> <jlarkin@highland_atwork_technology.com> wrote: >>> >>>> What's a good way to make a, say 2 or 3 GHz sinewave oscillator? I >>>> don't need extreme accuracy, and I'd like maybe 1 volt p-p. >>>> >>>> I was thinking a cheap MMIC with PCB delay line feedback. >>>> >>>> MiniCircuits VCOs are around $20, which isn't bad. >>>> >>>> The output would go into a PWM modulator and then an AC-coupled >>>> communications channel. >>> >>> hat are you trying to do ? >>> >>> Are you trying to transfer a very broad band DC based _analog_ signal >>> (say DC .. 500 MHz) over an AC link (say 2 GHz). >> >> >> That, or just ship a single-bit logic level over a telecom type link. >> It's just a shower musing, not serious yet. >> >>> >>> Why not simply frequency module a VCO ? Why PWM ? >>> >> >> FM is more work on both ends. Commercial VCOs have pitiful modulation >> bandwidths, kilohertz not gigahertz. PWM can be arbitrarily fast. >> >> For the logic level case, we'd want it to be fast with low jitter. >> Whatever modulation scheme is used, the time jitter should be a >> fraction of the "carrier" period. >> >> This problem is similar to the Shannon sampling theorem. A bandlimited >> signal can be sampled at some rate and reproduced perfectly from the >> sampled values. The trick is to have the modulation scheme be >> continuous and bandlimited such as to eliminate the jitter of the >> modulation/demod scheme. >> >> Wideband FM gets mathematically messy too. Ugly sidebands. >> >> PWM would be fairly easy to generate and detect. I've tested some 10 >> GBPS tosa/rosa optical links and they do transmit PWM, to various >> extents. Of course they go bonkers at extreme duty cycles. >> >> >> >> >> > >How about a very fast logic gate (or string of gates) moderated by a >delay line. Make one a NOR or NAND and that gets the PWM input? > >pigletA fast comparator could look at a sine wave and a DC level to make PWM at its output. Even a triangle if linearity is important, which is isn't to transmit a 1-bit digital state. A differential-input gate, like a 10EP part, is a decent comparator, cheaper and simpler than an ADCMP thing.
GHz oscillator
Started by ●April 27, 2021
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fredag den 30. april 2021 kl. 21.31.52 UTC+2 skrev John Larkin:> On Fri, 30 Apr 2021 11:10:12 -0700 (PDT), Lasse Langwadt Christensen > <lang...@fonz.dk> wrote: > > >fredag den 30. april 2021 kl. 19.51.58 UTC+2 skrev John Larkin: > >> On Fri, 30 Apr 2021 10:09:59 -0700 (PDT), Lasse Langwadt Christensen > >> <lang...@fonz.dk> wrote: > >> > >> >fredag den 30. april 2021 kl. 19.04.03 UTC+2 skrev John Larkin: > >> >> On Fri, 30 Apr 2021 19:54:36 +0300, upsid...@downunder.com wrote: > >> >> > >> >> >On Fri, 30 Apr 2021 08:45:30 -0700, jla...@highlandsniptechnology.com > >> >> >wrote: > >> >> > > >> >> >>On Fri, 30 Apr 2021 08:07:10 +0300, upsid...@downunder.com wrote: > >> >> >> > >> >> >>>On Tue, 27 Apr 2021 12:35:17 -0700, John Larkin > >> >> >>><jlarkin@highland_atwork_technology.com> wrote: > >> >> >>> > >> >> >>>>What's a good way to make a, say 2 or 3 GHz sinewave oscillator? I > >> >> >>>>don't need extreme accuracy, and I'd like maybe 1 volt p-p. > >> >> >>>> > >> >> >>>>I was thinking a cheap MMIC with PCB delay line feedback. > >> >> >>>> > >> >> >>>>MiniCircuits VCOs are around $20, which isn't bad. > >> >> >>>> > >> >> >>>>The output would go into a PWM modulator and then an AC-coupled > >> >> >>>>communications channel. > >> >> >>> > >> >> >>>hat are you trying to do ? > >> >> >>> > >> >> >>>Are you trying to transfer a very broad band DC based _analog_ signal > >> >> >>>(say DC .. 500 MHz) over an AC link (say 2 GHz). > >> >> >> > >> >> >> > >> >> >>That, or just ship a single-bit logic level over a telecom type link. > >> >> >>It's just a shower musing, not serious yet. > >> >> >> > >> >> >>> > >> >> >>>Why not simply frequency module a VCO ? Why PWM ? > >> >> >>> > >> >> >> > >> >> >>FM is more work on both ends. Commercial VCOs have pitiful modulation > >> >> >>bandwidths, kilohertz not gigahertz. PWM can be arbitrarily fast. > >> >> >> > >> >> >>For the logic level case, we'd want it to be fast with low jitter. > >> >> >>Whatever modulation scheme is used, the time jitter should be a > >> >> >>fraction of the "carrier" period. > >> >> > > >> >> >What about phase shifting keying (PSK) ? > >> >> How can you DC couple PSK? > >> >> > > >> >> >Just invert the output from the oscillator at input signal change. Of > >> >> >course, you have to establish the initial state somehow to be able to > >> >> >decode current state from only phase changes. > >> >> > > >> >> >To always know the state, you could use return to zero coding, i.e. a > >> >> >carrier at 0 degrees, a 0->1 transition as +90 degree phase change and > >> >> >1->0 input change as -90 degrees phase shift (QPSK). > >> >> > > >> >> >Also take look at Manchester coding. > >> >> > > >> >> Manchester is phase ambiguous! A long string of 1's looks just like a > >> >> long string of 0's. And the decode is clock synchronous, so has > >> >> massive jitter when shipping an arbitrary signal. > >> >> > >> >> PSK ditto. I want to modulate, not encode. > >> >> > >> >> AM/OOK won't work when the receiver has AGC. > >> > > >> >wouldn't your pwm be OOK? > >> No. It would be a fixed frequency continuous square wave of modulated > >> duty cycle. That does DC coupled transmission of an asynchronous > >> analog or logic-level baseband signal. > > > >so the ~2GHz it self have varying duty cycle? not ~2GHz on/off ? > Right. It shouldn't be difficult. > > OOK has the long-term receive threshold problem. > > > >> > >> The duty cycle can't get extreme or the optical receivers get unhappy. > >> 40/60 % seems conservative for a typical telecom rosa. I might look > >> into duty cycle modulation over an ethernet type path, twisted pairs > >> with magnetics. > > > >I guess with two pairs you could send the carrier on one pair to demodulate > >the other pair at the far end > AM with synchronous demodulation?or PM>PWM only needs one channel and a lowpass filter to demodulate.but then your channel will have varying DC
Reply by ●April 30, 20212021-04-30
John Larkin <jlarkin@highland_atwork_technology.com> wrote:> On Fri, 30 Apr 2021 20:43:08 +0200, Gerhard Hoffmann <dk4xp@arcor.de> > wrote: > >>Am 30.04.21 um 19:03 schrieb John Larkin: >>> On Fri, 30 Apr 2021 19:54:36 +0300, upsidedown@downunder.com wrote: >> >> >>>> What about phase shifting keying (PSK) ? >>> >>> How can you DC couple PSK? >> >>BPSK is: Ring mixer like MCL IE-500 >> >>RF port: input >>LO port: output >>IF port: modulation in >> >>Demodulation / bit sclicing happens in Squaring or Costas loop. >> >>Gerhard > > I don't want to send clocked digital data, I want to send an analog > level. > > Suppose the input to the transmitter (IF port here) is +0.5 volts. > That makes a carrier of some amplitude and phase. > > The receiver gets that carrier. The channel has attenuation. How does > the receiver know it's supposed to output +0.5 volts? > > It could guess the phase wrong and output -0.5 volts. Or not know the > channel attenuation and output +7 volts. > > If it sees an invariant sine wave for six weeks, or at powerup, is the > signal positive or negative?How about a 4 - 20 ma current loop? The transmission line is shielded if you are going to carry 2 GHz signals. You can terminate in 50 ohms to match the cable impedance. Then all you need is a wide bandwidth current source which should be easy. The output voltage is simply E = I * R. You can beat the bandwidth of PWM due to the filtering required at the receiver. Even extensive filtering leaves some ripple, which reduces the accuracy of data transmission. With controlled current, you don't have to worry about voltage drops along the transmission line. You can set a current value that lasts for years, even with multiple powerups. Unlike PWM, the overall accuracy is determined by relatively few components. -- The best designs occur in the theta state. - sw
Reply by ●April 30, 20212021-04-30
On Fri, 30 Apr 2021 13:26:39 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>fredag den 30. april 2021 kl. 21.31.52 UTC+2 skrev John Larkin: >> On Fri, 30 Apr 2021 11:10:12 -0700 (PDT), Lasse Langwadt Christensen >> <lang...@fonz.dk> wrote: >> >> >fredag den 30. april 2021 kl. 19.51.58 UTC+2 skrev John Larkin: >> >> On Fri, 30 Apr 2021 10:09:59 -0700 (PDT), Lasse Langwadt Christensen >> >> <lang...@fonz.dk> wrote: >> >> >> >> >fredag den 30. april 2021 kl. 19.04.03 UTC+2 skrev John Larkin: >> >> >> On Fri, 30 Apr 2021 19:54:36 +0300, upsid...@downunder.com wrote: >> >> >> >> >> >> >On Fri, 30 Apr 2021 08:45:30 -0700, jla...@highlandsniptechnology.com >> >> >> >wrote: >> >> >> > >> >> >> >>On Fri, 30 Apr 2021 08:07:10 +0300, upsid...@downunder.com wrote: >> >> >> >> >> >> >> >>>On Tue, 27 Apr 2021 12:35:17 -0700, John Larkin >> >> >> >>><jlarkin@highland_atwork_technology.com> wrote: >> >> >> >>> >> >> >> >>>>What's a good way to make a, say 2 or 3 GHz sinewave oscillator? I >> >> >> >>>>don't need extreme accuracy, and I'd like maybe 1 volt p-p. >> >> >> >>>> >> >> >> >>>>I was thinking a cheap MMIC with PCB delay line feedback. >> >> >> >>>> >> >> >> >>>>MiniCircuits VCOs are around $20, which isn't bad. >> >> >> >>>> >> >> >> >>>>The output would go into a PWM modulator and then an AC-coupled >> >> >> >>>>communications channel. >> >> >> >>> >> >> >> >>>hat are you trying to do ? >> >> >> >>> >> >> >> >>>Are you trying to transfer a very broad band DC based _analog_ signal >> >> >> >>>(say DC .. 500 MHz) over an AC link (say 2 GHz). >> >> >> >> >> >> >> >> >> >> >> >>That, or just ship a single-bit logic level over a telecom type link. >> >> >> >>It's just a shower musing, not serious yet. >> >> >> >> >> >> >> >>> >> >> >> >>>Why not simply frequency module a VCO ? Why PWM ? >> >> >> >>> >> >> >> >> >> >> >> >>FM is more work on both ends. Commercial VCOs have pitiful modulation >> >> >> >>bandwidths, kilohertz not gigahertz. PWM can be arbitrarily fast. >> >> >> >> >> >> >> >>For the logic level case, we'd want it to be fast with low jitter. >> >> >> >>Whatever modulation scheme is used, the time jitter should be a >> >> >> >>fraction of the "carrier" period. >> >> >> > >> >> >> >What about phase shifting keying (PSK) ? >> >> >> How can you DC couple PSK? >> >> >> > >> >> >> >Just invert the output from the oscillator at input signal change. Of >> >> >> >course, you have to establish the initial state somehow to be able to >> >> >> >decode current state from only phase changes. >> >> >> > >> >> >> >To always know the state, you could use return to zero coding, i.e. a >> >> >> >carrier at 0 degrees, a 0->1 transition as +90 degree phase change and >> >> >> >1->0 input change as -90 degrees phase shift (QPSK). >> >> >> > >> >> >> >Also take look at Manchester coding. >> >> >> > >> >> >> Manchester is phase ambiguous! A long string of 1's looks just like a >> >> >> long string of 0's. And the decode is clock synchronous, so has >> >> >> massive jitter when shipping an arbitrary signal. >> >> >> >> >> >> PSK ditto. I want to modulate, not encode. >> >> >> >> >> >> AM/OOK won't work when the receiver has AGC. >> >> > >> >> >wouldn't your pwm be OOK? >> >> No. It would be a fixed frequency continuous square wave of modulated >> >> duty cycle. That does DC coupled transmission of an asynchronous >> >> analog or logic-level baseband signal. >> > >> >so the ~2GHz it self have varying duty cycle? not ~2GHz on/off ? >> Right. It shouldn't be difficult. >> >> OOK has the long-term receive threshold problem. >> > >> >> >> >> The duty cycle can't get extreme or the optical receivers get unhappy. >> >> 40/60 % seems conservative for a typical telecom rosa. I might look >> >> into duty cycle modulation over an ethernet type path, twisted pairs >> >> with magnetics. >> > >> >I guess with two pairs you could send the carrier on one pair to demodulate >> >the other pair at the far end >> AM with synchronous demodulation? > >or PM > >>PWM only needs one channel and a lowpass filter to demodulate. > >but then your channel will have varying DCThe signal on an AC-coupled channel always averages zero. If you poke a PWM square wave through it, you get an asymmetric amplitude square wave with zero DC average. Telecom-type optical signals are usually transmitted by switching a laser on/off, following the digital input. The transmitters are usually AC coupled, so need continuous, roughly 50% digital activity to work right. That is typically received by a photodiode, an AC-coupled AGC amplifier, and a zero crossing detector, to typically make an AC-coupled differential CML output. Ethernet type signals are transformer coupled on both ends. That gets interesting to push a DC coupled signal through, theoretically and experimentally.
Reply by ●April 30, 20212021-04-30
On Fri, 30 Apr 2021 22:46:10 -0000 (UTC), Steve Wilson <spamme@not.com> wrote:>John Larkin <jlarkin@highland_atwork_technology.com> wrote: > >> On Fri, 30 Apr 2021 20:43:08 +0200, Gerhard Hoffmann <dk4xp@arcor.de> >> wrote: >> >>>Am 30.04.21 um 19:03 schrieb John Larkin: >>>> On Fri, 30 Apr 2021 19:54:36 +0300, upsidedown@downunder.com wrote: >>> >>> >>>>> What about phase shifting keying (PSK) ? >>>> >>>> How can you DC couple PSK? >>> >>>BPSK is: Ring mixer like MCL IE-500 >>> >>>RF port: input >>>LO port: output >>>IF port: modulation in >>> >>>Demodulation / bit sclicing happens in Squaring or Costas loop. >>> >>>Gerhard >> >> I don't want to send clocked digital data, I want to send an analog >> level. >> >> Suppose the input to the transmitter (IF port here) is +0.5 volts. >> That makes a carrier of some amplitude and phase. >> >> The receiver gets that carrier. The channel has attenuation. How does >> the receiver know it's supposed to output +0.5 volts? >> >> It could guess the phase wrong and output -0.5 volts. Or not know the >> channel attenuation and output +7 volts. >> >> If it sees an invariant sine wave for six weeks, or at powerup, is the >> signal positive or negative? > >How about a 4 - 20 ma current loop? The transmission line is shielded if >you are going to carry 2 GHz signals. You can terminate in 50 ohms to match >the cable impedance. Then all you need is a wide bandwidth current source >which should be easy. The output voltage is simply E = I * R. > >You can beat the bandwidth of PWM due to the filtering required at the >receiver. Even extensive filtering leaves some ripple, which reduces the >accuracy of data transmission. > >With controlled current, you don't have to worry about voltage drops along >the transmission line. You can set a current value that lasts for years, >even with multiple powerups. Unlike PWM, the overall accuracy is determined >by relatively few components.I'm interested in inherently AC-coupled channels, namely telecom type fiber links or ethernet-style transformer-couples twisted pairs. We already sell fast DC coupled fiber links, laser on/off things. But the receive threshold has to be manually set and the effective threshold varies with path attenuation. Somebody tie-wraps a fiber down, or adds a bulkhead feedthrough, and the threshold is trashed.
Reply by ●April 30, 20212021-04-30
lørdag den 1. maj 2021 kl. 01.19.47 UTC+2 skrev John Larkin:> On Fri, 30 Apr 2021 13:26:39 -0700 (PDT), Lasse Langwadt Christensen > <lang...@fonz.dk> wrote: > > >fredag den 30. april 2021 kl. 21.31.52 UTC+2 skrev John Larkin: > >> On Fri, 30 Apr 2021 11:10:12 -0700 (PDT), Lasse Langwadt Christensen > >> <lang...@fonz.dk> wrote: > >> > >> >fredag den 30. april 2021 kl. 19.51.58 UTC+2 skrev John Larkin: > >> >> On Fri, 30 Apr 2021 10:09:59 -0700 (PDT), Lasse Langwadt Christensen > >> >> <lang...@fonz.dk> wrote: > >> >> > >> >> >fredag den 30. april 2021 kl. 19.04.03 UTC+2 skrev John Larkin: > >> >> >> On Fri, 30 Apr 2021 19:54:36 +0300, upsid...@downunder.com wrote: > >> >> >> > >> >> >> >On Fri, 30 Apr 2021 08:45:30 -0700, jla...@highlandsniptechnology.com > >> >> >> >wrote: > >> >> >> > > >> >> >> >>On Fri, 30 Apr 2021 08:07:10 +0300, upsid...@downunder.com wrote: > >> >> >> >> > >> >> >> >>>On Tue, 27 Apr 2021 12:35:17 -0700, John Larkin > >> >> >> >>><jlarkin@highland_atwork_technology.com> wrote: > >> >> >> >>> > >> >> >> >>>>What's a good way to make a, say 2 or 3 GHz sinewave oscillator? I > >> >> >> >>>>don't need extreme accuracy, and I'd like maybe 1 volt p-p. > >> >> >> >>>> > >> >> >> >>>>I was thinking a cheap MMIC with PCB delay line feedback. > >> >> >> >>>> > >> >> >> >>>>MiniCircuits VCOs are around $20, which isn't bad. > >> >> >> >>>> > >> >> >> >>>>The output would go into a PWM modulator and then an AC-coupled > >> >> >> >>>>communications channel. > >> >> >> >>> > >> >> >> >>>hat are you trying to do ? > >> >> >> >>> > >> >> >> >>>Are you trying to transfer a very broad band DC based _analog_ signal > >> >> >> >>>(say DC .. 500 MHz) over an AC link (say 2 GHz). > >> >> >> >> > >> >> >> >> > >> >> >> >>That, or just ship a single-bit logic level over a telecom type link. > >> >> >> >>It's just a shower musing, not serious yet. > >> >> >> >> > >> >> >> >>> > >> >> >> >>>Why not simply frequency module a VCO ? Why PWM ? > >> >> >> >>> > >> >> >> >> > >> >> >> >>FM is more work on both ends. Commercial VCOs have pitiful modulation > >> >> >> >>bandwidths, kilohertz not gigahertz. PWM can be arbitrarily fast. > >> >> >> >> > >> >> >> >>For the logic level case, we'd want it to be fast with low jitter. > >> >> >> >>Whatever modulation scheme is used, the time jitter should be a > >> >> >> >>fraction of the "carrier" period. > >> >> >> > > >> >> >> >What about phase shifting keying (PSK) ? > >> >> >> How can you DC couple PSK? > >> >> >> > > >> >> >> >Just invert the output from the oscillator at input signal change. Of > >> >> >> >course, you have to establish the initial state somehow to be able to > >> >> >> >decode current state from only phase changes. > >> >> >> > > >> >> >> >To always know the state, you could use return to zero coding, i.e. a > >> >> >> >carrier at 0 degrees, a 0->1 transition as +90 degree phase change and > >> >> >> >1->0 input change as -90 degrees phase shift (QPSK). > >> >> >> > > >> >> >> >Also take look at Manchester coding. > >> >> >> > > >> >> >> Manchester is phase ambiguous! A long string of 1's looks just like a > >> >> >> long string of 0's. And the decode is clock synchronous, so has > >> >> >> massive jitter when shipping an arbitrary signal. > >> >> >> > >> >> >> PSK ditto. I want to modulate, not encode. > >> >> >> > >> >> >> AM/OOK won't work when the receiver has AGC. > >> >> > > >> >> >wouldn't your pwm be OOK? > >> >> No. It would be a fixed frequency continuous square wave of modulated > >> >> duty cycle. That does DC coupled transmission of an asynchronous > >> >> analog or logic-level baseband signal. > >> > > >> >so the ~2GHz it self have varying duty cycle? not ~2GHz on/off ? > >> Right. It shouldn't be difficult. > >> > >> OOK has the long-term receive threshold problem. > >> > > >> >> > >> >> The duty cycle can't get extreme or the optical receivers get unhappy. > >> >> 40/60 % seems conservative for a typical telecom rosa. I might look > >> >> into duty cycle modulation over an ethernet type path, twisted pairs > >> >> with magnetics. > >> > > >> >I guess with two pairs you could send the carrier on one pair to demodulate > >> >the other pair at the far end > >> AM with synchronous demodulation? > > > >or PM > > > >>PWM only needs one channel and a lowpass filter to demodulate. > > > >but then your channel will have varying DC > The signal on an AC-coupled channel always averages zero. If you poke > a PWM square wave through it, you get an asymmetric amplitude square > wave with zero DC average.unless that channel have limited bandwidth, no?
Reply by ●May 1, 20212021-05-01
On Fri, 30 Apr 2021 18:51:20 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>l�rdag den 1. maj 2021 kl. 01.19.47 UTC+2 skrev John Larkin: >> On Fri, 30 Apr 2021 13:26:39 -0700 (PDT), Lasse Langwadt Christensen >> <lang...@fonz.dk> wrote: >> >> >fredag den 30. april 2021 kl. 21.31.52 UTC+2 skrev John Larkin: >> >> On Fri, 30 Apr 2021 11:10:12 -0700 (PDT), Lasse Langwadt Christensen >> >> <lang...@fonz.dk> wrote: >> >> >> >> >fredag den 30. april 2021 kl. 19.51.58 UTC+2 skrev John Larkin: >> >> >> On Fri, 30 Apr 2021 10:09:59 -0700 (PDT), Lasse Langwadt Christensen >> >> >> <lang...@fonz.dk> wrote: >> >> >> >> >> >> >fredag den 30. april 2021 kl. 19.04.03 UTC+2 skrev John Larkin: >> >> >> >> On Fri, 30 Apr 2021 19:54:36 +0300, upsid...@downunder.com wrote: >> >> >> >> >> >> >> >> >On Fri, 30 Apr 2021 08:45:30 -0700, jla...@highlandsniptechnology.com >> >> >> >> >wrote: >> >> >> >> > >> >> >> >> >>On Fri, 30 Apr 2021 08:07:10 +0300, upsid...@downunder.com wrote: >> >> >> >> >> >> >> >> >> >>>On Tue, 27 Apr 2021 12:35:17 -0700, John Larkin >> >> >> >> >>><jlarkin@highland_atwork_technology.com> wrote: >> >> >> >> >>> >> >> >> >> >>>>What's a good way to make a, say 2 or 3 GHz sinewave oscillator? I >> >> >> >> >>>>don't need extreme accuracy, and I'd like maybe 1 volt p-p. >> >> >> >> >>>> >> >> >> >> >>>>I was thinking a cheap MMIC with PCB delay line feedback. >> >> >> >> >>>> >> >> >> >> >>>>MiniCircuits VCOs are around $20, which isn't bad. >> >> >> >> >>>> >> >> >> >> >>>>The output would go into a PWM modulator and then an AC-coupled >> >> >> >> >>>>communications channel. >> >> >> >> >>> >> >> >> >> >>>hat are you trying to do ? >> >> >> >> >>> >> >> >> >> >>>Are you trying to transfer a very broad band DC based _analog_ signal >> >> >> >> >>>(say DC .. 500 MHz) over an AC link (say 2 GHz). >> >> >> >> >> >> >> >> >> >> >> >> >> >> >>That, or just ship a single-bit logic level over a telecom type link. >> >> >> >> >>It's just a shower musing, not serious yet. >> >> >> >> >> >> >> >> >> >>> >> >> >> >> >>>Why not simply frequency module a VCO ? Why PWM ? >> >> >> >> >>> >> >> >> >> >> >> >> >> >> >>FM is more work on both ends. Commercial VCOs have pitiful modulation >> >> >> >> >>bandwidths, kilohertz not gigahertz. PWM can be arbitrarily fast. >> >> >> >> >> >> >> >> >> >>For the logic level case, we'd want it to be fast with low jitter. >> >> >> >> >>Whatever modulation scheme is used, the time jitter should be a >> >> >> >> >>fraction of the "carrier" period. >> >> >> >> > >> >> >> >> >What about phase shifting keying (PSK) ? >> >> >> >> How can you DC couple PSK? >> >> >> >> > >> >> >> >> >Just invert the output from the oscillator at input signal change. Of >> >> >> >> >course, you have to establish the initial state somehow to be able to >> >> >> >> >decode current state from only phase changes. >> >> >> >> > >> >> >> >> >To always know the state, you could use return to zero coding, i.e. a >> >> >> >> >carrier at 0 degrees, a 0->1 transition as +90 degree phase change and >> >> >> >> >1->0 input change as -90 degrees phase shift (QPSK). >> >> >> >> > >> >> >> >> >Also take look at Manchester coding. >> >> >> >> > >> >> >> >> Manchester is phase ambiguous! A long string of 1's looks just like a >> >> >> >> long string of 0's. And the decode is clock synchronous, so has >> >> >> >> massive jitter when shipping an arbitrary signal. >> >> >> >> >> >> >> >> PSK ditto. I want to modulate, not encode. >> >> >> >> >> >> >> >> AM/OOK won't work when the receiver has AGC. >> >> >> > >> >> >> >wouldn't your pwm be OOK? >> >> >> No. It would be a fixed frequency continuous square wave of modulated >> >> >> duty cycle. That does DC coupled transmission of an asynchronous >> >> >> analog or logic-level baseband signal. >> >> > >> >> >so the ~2GHz it self have varying duty cycle? not ~2GHz on/off ? >> >> Right. It shouldn't be difficult. >> >> >> >> OOK has the long-term receive threshold problem. >> >> > >> >> >> >> >> >> The duty cycle can't get extreme or the optical receivers get unhappy. >> >> >> 40/60 % seems conservative for a typical telecom rosa. I might look >> >> >> into duty cycle modulation over an ethernet type path, twisted pairs >> >> >> with magnetics. >> >> > >> >> >I guess with two pairs you could send the carrier on one pair to demodulate >> >> >the other pair at the far end >> >> AM with synchronous demodulation? >> > >> >or PM >> > >> >>PWM only needs one channel and a lowpass filter to demodulate. >> > >> >but then your channel will have varying DC >> The signal on an AC-coupled channel always averages zero. If you poke >> a PWM square wave through it, you get an asymmetric amplitude square >> wave with zero DC average. > >unless that channel have limited bandwidth, no?Of course. A typical SFP module might be rated for 10 GBPS (passes a 5 GHz square wave) and only work down to a couple of MHz on the low end. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●May 1, 20212021-05-01
On Tue, 27 Apr 2021 12:35:17 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote:>What's a good way to make a, say 2 or 3 GHz sinewave oscillator? I >don't need extreme accuracy, and I'd like maybe 1 volt p-p. > >I was thinking a cheap MMIC with PCB delay line feedback. > >MiniCircuits VCOs are around $20, which isn't bad. > >The output would go into a PWM modulator and then an AC-coupled >communications channel.Here's a 2 GHz oscillator with PWM modulation. First cut, needs work. Costs about $2.50. Version 4 SHEET 1 880 680 WIRE 0 -176 -640 -176 WIRE 144 -176 0 -176 WIRE -640 -128 -640 -176 WIRE 0 -128 0 -176 WIRE 144 -112 144 -176 WIRE -640 32 -640 -48 WIRE -592 32 -640 32 WIRE -464 32 -512 32 WIRE -336 32 -464 32 WIRE -224 32 -272 32 WIRE -144 32 -224 32 WIRE 0 32 0 -48 WIRE 0 32 -144 32 WIRE 144 32 144 -32 WIRE -144 80 -144 32 WIRE -640 96 -640 32 WIRE -416 96 -640 96 WIRE -384 96 -416 96 WIRE -640 112 -640 96 WIRE 0 112 0 32 WIRE -464 192 -464 32 WIRE -464 192 -592 192 WIRE -384 192 -384 96 WIRE -336 192 -384 192 WIRE -144 192 -144 160 WIRE -144 192 -272 192 WIRE -48 192 -144 192 WIRE -464 240 -464 192 WIRE -144 240 -144 192 WIRE -640 272 -640 208 WIRE 0 272 0 208 WIRE -464 352 -464 320 WIRE -384 352 -464 352 WIRE -224 352 -384 352 WIRE -464 384 -464 352 WIRE -144 384 -144 320 WIRE -224 400 -224 352 WIRE -192 400 -224 400 WIRE -192 448 -224 448 WIRE -464 512 -464 464 WIRE -224 512 -224 448 WIRE -144 512 -144 464 FLAG 144 32 0 FLAG -640 272 0 FLAG 0 272 0 FLAG -416 96 A FLAG -224 32 B FLAG -464 512 0 FLAG -224 512 0 FLAG -144 512 0 FLAG -384 352 PWM SYMBOL mesfet -48 112 R0 WINDOW 0 81 19 Left 2 WINDOW 3 59 55 Left 2 SYMATTR InstName Z1 SYMATTR Value SAV551 SYMBOL voltage 144 -128 R0 WINDOW 0 59 34 Left 2 WINDOW 3 56 69 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 2.5 SYMBOL mesfet -592 112 M0 WINDOW 0 -56 24 Left 2 WINDOW 3 -94 54 Left 2 SYMATTR InstName Z2 SYMATTR Value SAV551 SYMBOL cap -272 16 R90 WINDOW 0 -41 28 VBottom 2 WINDOW 3 -37 27 VTop 2 SYMATTR InstName C1 SYMATTR Value 2p SYMBOL cap -272 176 R90 WINDOW 0 -44 26 VBottom 2 WINDOW 3 -39 26 VTop 2 SYMATTR InstName C2 SYMATTR Value 2p SYMBOL res -496 16 R90 WINDOW 0 -38 55 VBottom 2 WINDOW 3 -36 53 VTop 2 SYMATTR InstName R1 SYMATTR Value 200 SYMBOL res -128 176 R180 WINDOW 0 55 72 Left 2 WINDOW 3 50 41 Left 2 SYMATTR InstName R3 SYMATTR Value 200 SYMBOL res -16 -144 R0 WINDOW 0 -60 43 Left 2 WINDOW 3 -58 72 Left 2 SYMATTR InstName R4 SYMATTR Value 40 SYMBOL res -656 -144 R0 WINDOW 0 52 40 Left 2 WINDOW 3 53 70 Left 2 SYMATTR InstName R5 SYMATTR Value 40 SYMBOL voltage -464 368 R0 WINDOW 0 -86 66 Left 2 WINDOW 3 -288 112 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PULSE(0.2 5 1n 25n 0 1) SYMBOL res -480 224 R0 WINDOW 0 -56 40 Left 2 WINDOW 3 -55 75 Left 2 SYMATTR InstName R2 SYMATTR Value 2k SYMBOL e -144 368 R0 WINDOW 0 68 35 Left 2 WINDOW 3 70 71 Left 2 SYMATTR InstName E1 SYMATTR Value -1 SYMBOL res -160 224 R0 WINDOW 0 -56 40 Left 2 WINDOW 3 -55 75 Left 2 SYMATTR InstName R6 SYMATTR Value 2k TEXT 16 384 Left 2 !.MODEL SAV551 NMF( vto=0.08, Beta=0.3,\n+ Lambda=0.07, Alpha=4 B=0.8, Pb=0.7,\n+ Cgs=0.997E-12, Cgd=0.176E-12, Rd=0.084,\n+ Rs=0.054, Kf=5e-11, Af=2) TEXT 208 288 Left 2 !.tran 0 25n 0 100f TEXT 192 168 Left 2 ;2 GHz PWM Oscillator TEXT 216 216 Left 2 ;JL Apr 30 2021 -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●May 1, 20212021-05-01
On Friday, April 30, 2021 at 4:28:32 PM UTC-7, John Larkin wrote:> I'm interested in inherently AC-coupled channels, namely telecom type > fiber links or ethernet-style transformer-couples twisted pairs. > > We already sell fast DC coupled fiber links, laser on/off things. But > the receive threshold has to be manually set and the effective > threshold varies with path attenuation. Somebody tie-wraps a fiber > down, or adds a bulkhead feedthrough, and the threshold is trashed.If you want a continuous signal but only have AC channels, consider a sine/cosine oscillator, or multiphase oscillator, where the sum of the squares of the signals is constant (good for gain control) but the frequency can mismatch against a local oscillator (giving you an FM decoded value, or phase-shift value if that's preferable). Thermistor sensing of a sine and cosine pair of heaters is a fairly easy way to do gain control.
Reply by ●May 1, 20212021-05-01
On 30/04/2021 23:46, Steve Wilson wrote:> > You can beat the bandwidth of PWM due to the filtering required at the > receiver. Even extensive filtering leaves some ripple, which reduces the > accuracy of data transmission. >Filtering PWM can be made less onerous using Woodward's cancellation scheme. <www.dropbox.com/s/997fixfek6afwga/woodward_dac_precision_ifd.pdf?raw=1> SED last discussed this on 19 Feb 2021 under title "PWM Output With RC Coupled Inverted Signal" I wonder if at 2GHz the inverter could be replaced with a 180deg length delay line? Could make very simple demodulator. piglet
