[time-nuts] Sine to square wave converter Phase Noise

Magnus Danielson magnus at rubidium.dyndns.org
Tue Jul 29 10:07:50 EDT 2014


One could possibly use another transistor pair in front of this one.

For lower rate signals, it is a great "finalizer" solution to a 
step-wise increase in bandwidth and slew-rate.

Cheers,
Magnus

On 07/29/2014 02:54 PM, bruce at ko4bb.com wrote:
> I merely used the evaluation board which has a capacitively coupled input.
> The transformer coupled input circuit using a 1:4 (turns ratio) step up
> transformer
> as depicted on the datasheet should reduce the PN floor by at least 3dB for
> 10MHz input.
>
> Bruce
>> On July 29, 2014 at 7:30 AM "David C. Partridge"
>> <david.partridge at perdrix.co.uk> wrote:
>>
>>
>> Bruce,
>>
>> Thank you, that was very useful information. If I ever do a re-spin of the
>> divider I will likely use the LTC6957-3 or -4 instead of the ADCMP600 (I
>> would need interest for at least 40 boards to be able to do this at anything
>> like an economic price).
>>
>> Will you be putting the full details of the circuit you used up on Didier's
>> web site? Did you use a transformer based circuit similar to Design Note
>> 514 or just an input capacitor?
>>
>> Regards,
>> David Partridge
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of bruce at ko4bb.com
>> Sent: 29 July 2014 12:00
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Sine to square wave converter Phase Noise
>>
>> Sorry, I meant the LTC6957-4 of course._SELA = l FILTA = L FILTB = H ie an
>> input stage BW of 160MHz as recommended for a 10MHz + 10dBm input.
>>
>> Input for the HX4210 was +14dBm.
>>
>> Comparator was that used in David Partridge's programmable divider (includes
>> the
>> 74AC04 buffers).
>>
>> Bruce
>>
>>> On July 29, 2014 at 5:37 AM Magnus Danielson
>>> <magnus at rubidium.dyndns.org>
>>> wrote:
>>>
>>>
>>> You alternate LTC7957-4 and LTC6957-4 and it is only the later that
>> exists.
>>>
>>> The LTC6957-4 has a single-stage amplifier stage input, with somewhat
>>> programmable bandwidth. I assume you used the 50 MHz BW setting.
>>>
>>> Cheers,
>>> Magnus
>>>
>>> On 07/29/2014 10:55 AM, bruce at ko4bb.com wrote:
>>>> Recently I have been comparing the phase noise of the HOlzworth
>>>> HX4210 and the LTC7957-4.
>>>> I have found that the performance of these devices is comparable
>>>> with a 10MHz sinewave input with a PN noise floor below -160dBc/Hz.
>>>> For offsets below 100Hz the LTC6957-4 is quieter and for offsets
>>>> below 50Hz or so is lower than that of my measurement setup.
>>>> I merely mounted the LTC evaluation board in a diecast metal box to
>>>> reduce the effect of air currents on the LTC7957-4 and used an ultra
>>>> low noise 3.3V power supply (Abracon) to minimise the power supply
>>>> contribution to the measured phase noise.
>>>> Achieving a phase noise performance equal to that on the datasheet
>>>> was relatively easy.
>>>> In fact for low offsets the phase noise is lower than that shown on
>>>> the datasheet.
>>>>
>>>> I've also measured the phase noise of a comparator based sine to
>>>> CMOS converter and its PN floor is about 20dB higher than that of
>>>> the LTC6957.
>>>> On completion of measurements PN plots for the various sine to
>>>> square conveters tested will be added to the web pages I maintain on
>>>> Didiers site..
>>>>
>>>>
>>>> Bruce
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