On Tuesday, April 27, 2021 at 12:35:27 PM UTC-7, John Larkin 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.
> Piglet <erichpwagner@hotmail.com> wrote:
>
>> 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
>
> Thanks for the link. ISTR another analysis with actual waveforms.
>
> However, doing this at 3 GHz might be a problem.
On Sat, 1 May 2021 15:45:43 -0000 (UTC), Steve Wilson <spamme@not.com>
wrote:
>Piglet <erichpwagner@hotmail.com> wrote:
>
>> 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
>
>Thanks for the link. ISTR another analysis with actual waveforms.
>
>However, doing this at 3 GHz might be a problem.
Exactly. Just LC lowpass filtering was what I had in mind.
--
John Larkin Highland Technology, Inc
The best designs are necessarily accidental.
Reply by ●May 1, 20212021-05-01
On Sat, 01 May 2021 11:15:57 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:
>On Fri, 30 Apr 2021 16:19:36 -0700, John Larkin
><jlarkin@highland_atwork_technology.com> wrote:
>
>>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 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.
>>
>>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.
>
>I can speak to how optical Ethernet ensures that their signals can be
>transformer-coupled, regardless of what data is sent.
Optical ethernet is almost always SFP modules. Their i/o is capacitive
coupled differential CML, no transformers.
>
>The basic trick is that the code space of the line symbols is large
>enough that there are at minimum two line symbols that can be used to
>represent each possible data symbol (or control symbol). The line
>symbols are sent by OOK of the laser, it taking multiple on-off
>flashes to encode each line symbol. The transmitter keeps a running
>sum of the ones and zeros sent, and chooses which of the pair of line
>symbols to use depending on the running sum - if the sum is growing in
>one direction, the chosen symbols will drive the sum back towards zero
>average.
That's 8b10b or longer versions. The idea is to keep the 1/0 balance
exact long-term.
I want to send PWM, which doesn't, which is why it's interesting.
>
>There is a founding article that I read twenty years ago on the design
>of such codes. If I recall, this was invented at IBM. While I may
>have a copy of that article, I'll probably never find it now.
>
>Joe Gwinn
A typical FPGA serdes engine natively does 8b10b and longer balanced
codes. We have used the serdes engines to make PWM and programmable
pulses too. You have to get inside the serdes blocks and work near the
end.
--
John Larkin Highland Technology, Inc
The best designs are necessarily accidental.
Reply by Steve Wilson●May 1, 20212021-05-01
Piglet <erichpwagner@hotmail.com> wrote:
> 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
Thanks for the link. ISTR another analysis with actual waveforms.
However, doing this at 3 GHz might be a problem.
--
The best designs occur in the theta state. - sw
Reply by Joe Gwinn●May 1, 20212021-05-01
On Fri, 30 Apr 2021 16:19:36 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:
>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 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.
>
>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.
I can speak to how optical Ethernet ensures that their signals can be
transformer-coupled, regardless of what data is sent.
The basic trick is that the code space of the line symbols is large
enough that there are at minimum two line symbols that can be used to
represent each possible data symbol (or control symbol). The line
symbols are sent by OOK of the laser, it taking multiple on-off
flashes to encode each line symbol. The transmitter keeps a running
sum of the ones and zeros sent, and chooses which of the pair of line
symbols to use depending on the running sum - if the sum is growing in
one direction, the chosen symbols will drive the sum back towards zero
average.
There is a founding article that I read twenty years ago on the design
of such codes. If I recall, this was invented at IBM. While I may
have a copy of that article, I'll probably never find it now.
Joe Gwinn
Reply by Piglet●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
Reply by whit3rd●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 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 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.