[time-nuts] Sub-ps delay line
time at radio.sent.com
Thu Feb 9 01:59:17 EST 2017
Have you considered an I/Q phase shifterr? Signals in RF systems are
commonly phase shifted by using an I/Q quadrature modulator. Here is
how this works:
Apply the source sinewave signal to a quadrature hybrid (or some other
network which produces two outputs with a precise 90 degree phase
relationship between the outputs). Each output goes to the LO port of a
separate double balanced mixer. The IF ports of the two mixers are fed
with two DC signal (one for I control and the other for Q control). The
RF output ports of the two mixers are summed and this produces the
output sinewave signal. This complete system is commonly sold as an "I/Q
modulator" block. By using sine and cosine lookup tables to specify the
I and Q voltages you can generate a vector at any phase on the unit
circle (from a trigonometric point of view). This is the same technique
used to generate most digital modulation (QPSK, 8PSK, QAM, etc.), but in
this case the envelope is kept constant by insuring that the I and Q
signals meet the Pythagorean identity (I^2 + Q^2 = 1, scaled
appropriately). The sine and cosine functions are what is needed to map
the phase angle to I and Q signals which provide a constant amplitude as
the phase is shifted.
Here is an example for an I/Q modulator IC which works from 5 MHz
to 1.6 GHz:
Bill Byrom N5BB
On Wed, Feb 8, 2017, at 05:25 AM, Mattia Rizzi wrote:
> thank you all for the answers!
> The description I gave in the first email is a simplification of the
> system. The delay line is used to phase-match the clocks of a
> measurement system. Each board feature an ADC and a DAC. You
> can see it
> a distributed RF acquisition system, with microwave requirements
> on phase
> matching. The delay line is used ALSO to correctly align the
> clocks for
> ADCs, since each IC has an unknown Aperture Delay (PVT kicks in).
> Unfortunately I cannot change the voltage references to introduces a
> variable delay. That's also why I would like to have a delay
> line rather
> than a set-and-forget solution: I can compensate for PVT of the ADC
> as well.
> About temperature variation: LTC6957-1 is excellent, 0.1ps/C of
> delay change. I still have to check with Linear if this figure
> is valid
> also if you don't use BOTH (P and N) output clock lines. I'm
> not sure to
> use a balun (such as Minicircuit ADT2-1) for differential-to-single-
> conversion because I dont want to introduce additional tempco.
> Unfortunately, Mini-circuit has no data about that. The
> varactor itself
> a slight tempco, but the overall tempco should be below 1 ps/C.
> About voltage & supply variations: I'm planning to use a
> dedicate LDO for
> the delay line. LTC6957-1 has a maximum of 50ps/V propagation delay
> variation, I'm expecting to use an LDO with <1 mV/C of regulation
> stability (LT3045 has less than 100uV over 20 degree variation,
> but it's
> bit expensive). Again, I don't know if the 50ps/V figure is
> still valid
> using only one output, but since LVPECL output stages are done using a
> always in the active region, I'm expecting an isolation from the power
> supply voltage.
>> My first thought would be to use a pair of couplers before and
>> after the
> delay line and bring it into a mixer to serve as a phase detector such
> you can create a control loop to stabilize delay. This way you get a
> on the temperature variations.
> Thanks! Do you know a phase detector with such requirements on
> checked Mini-circuit but they don't have factory data on the
> stability of
> their products. Also, my signals are clocks rather than pure
>> I would also advise you take a look at how well you can maintain your
> system impedance, say 50 Ohms. For example, I have seen about
> 100's ps
> phase difference on a 10 MHz reference, using one BNC female-female
> versus another
> Yes, this is a calibration issue (repeatability) to be
> investigated, but
> since microwave systems have the same issues I hope there's
> already a way
> to how achieve that.
> Thank you!
> 2017-02-07 23:43 GMT+01:00 Magnus Danielson
> <magnus at rubidium.dyndns.org>:
>> My first thought would be to use a pair of couplers before and
>> after the
>> delay line and bring it into a mixer to serve as a phase detector
>> such that
>> you can create a control loop to stabilize delay. This way you get
>> a handle
>> on the temperature variations.
>> There is trombone delays that can be used. They seem to reach
>> that level
>> of resolution.
>> There is microstepper boxes, but usually they operate on 5 or 10 MHz.
>> There is multiple ways to design delays for CW signals,
>> microsteppers uses
>> various forms of gear-boxes and programmable generators. Chips
>> either use
>> gate delays or programmable comparator vs. ramp of some form.
>> Ensuring temperature stability and drift limits is however always
>> an issue.
>> Delay loop oscillator for calibration can be done, but biases can be
>> problematic, so a number of different setups needs to be done
>> to build
>> confidence. It's a combinatorial exercise which is quite interesting.
>> On 02/07/2017 05:13 PM, Mattia Rizzi wrote:
>>> I'm looking/designing a sub-ps delay line with very high stability.
>>> Basically it has microwave requirements on phase matching.
>>> The main features that such delay line should have are:
>>> - sub-ps resolution and about 1 ns range
>>> - High stability, must not drift more than 2ps/year, preferably
>>> - Temperature coefficient (tempco) below 1 ps/celsius
>>> - Low phase noise floor, target random jitter below 100 fs RSM from
>>> to 1MHz.
>>> - flicker noise below -90dBc at 1Hz (100MHz carrier)
>>> - cheap (below 50 euros) and PCB integrable
>>> - optional: autocalibration or a way to check calibration health
>>> over time
>>> (checking the oscillation frequency of the delay line connected as
>>> Operating conditions: The delay line will be used for RF
>>> where the clock signals (100-200MHz) must stay in +/- 10 ps error
>>> Since timing jitter (wander) is 1.6ps RMS, the delay line must
>>> be very
>>> accurate, with maximum of +/- 3ps of delay uncertainty. The delay
>>> line is
>>> used to phase-match the clock outputs at factory, hence will not be
>>> anymore modified (or for only fine corrections, tens of
>>> picoseconds). The
>>> factory calibration compensates for the delay line and PCB
>>> process/production variations. The boards will operate at
>>> almost same
>>> temperature and humidity levels over years of continuous running.
>>> Circuit constrains: The delay line is fed with an AC-coupled
>>> LVPECL clock
>>> output (only P output used) and should provides a single-ended
>>> AC clock
>>> output signal.
>>> Indeed, no commercial chip fits into these requirements.
>>> My idea is to use an RC filter to delay the input clock signal and
>>> then to
>>> restore the clock edges with a LTC6957-1 (LVPECL outputs).
>>> The RC filter would be realized using a varactor (Skyworks SMVA1470-
>>> and a 16-bit DAC to control the voltage bias (+ stable voltage
>>> I already checked the values, and sub-ps resolution seems easily
>>> achievable. The solution requires a factory calibration due to the
>>> non-linear behavior of the varactor, but since I only need small
>>> adjustments, this is not a problem.
>>> The problem is to guarantee the calibration over years of operation.
>>> Since a femtofarad parasitic capacitance can change the delay, I
>>> thought about protecting the delay line with some kind of resin
>>> and/or a RF cage to protect it from dirt and moisture.
>>> One of the issue is aging. I derived a typical varactor aging from
>>> oscillators (no varactor manufacturer knows the effects of aging
>>> on its
>>> products, apparently) and it's still good. But the aging of LTC6957
>>> is not
>>> Is the PCB fabrication using microwave requirements on the
>>> Based on your experience, do you think that such delay line can
>>> requirements listed above, especially stability?
>>> Am I missing something?
>>> Thank you!
>>> Mattia Rizzi
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/m
>>> and follow the instructions there.
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/m
>> and follow the instructions there.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> and follow the instructions there.
More information about the time-nuts