[time-nuts] Advanced 5 to 10 MHz doubler

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Jun 14 19:00:16 UTC 2011 

Luciano followed this up off list and found that the suggested 
improvements (and others) worked well.
The performance now closely mimics that of the simulations.
Final results:

Input range +6 to +13 dBm
Gain 0dB ± 1 dB on the input range.
Output harmonics and subharmonics -60 dBc

He intends to write an article on it.

As yet he hasn't been able to measure the phase noise as this requires 
using a pair of doublers with their outputs in phase quadrature.

Bruce

paul swed wrote:
> Lets see feb to june. Time to restart this thread.
> I found this a very interesting thread and finally ordered the transformers
> from mini circuits. Needed some other parts and had enough of an order to
> make sense.
> I do plan to build the circuit and try some of the comments suggested to see
> what happens.
> Though this may take a bit of time. Lots of other things to work on.
> Regards
> Paul
> WB8TSL
>
> On Wed, Feb 16, 2011 at 9:11 AM, paul swed<paulswedb at gmail.com>  wrote:
>
>    
>> This has been a great read.
>> Though I don't have a need at the moment. I may assemble this with the
>> various comments just to try it out. Dead bug style.
>> Regards
>>
>>
>> On Wed, Feb 16, 2011 at 8:46 AM, Paramithiotti, Luciano Paolo S<
>> luciano.paramithiotti at hp.com>  wrote:
>>
>>      
>>> Bruce,
>>> I have collected yours comments, I hope they will be usefull for my next
>>> doubler version.
>>> A question: do you have ever made a physical doubler like this? if so, can
>>> you show us the schematic, photos and results of measurements made?
>>>
>>> Luciano
>>>
>>> Luciano P. S. Paramithiotti
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>>> Behalf Of Bruce Griffiths
>>> Sent: martedì 15 febbraio 2011 22.19
>>> To: Discussion of precise time and frequency measurement
>>> Subject: Re: [time-nuts] Advanced 5 to 10 MHz doubler
>>>
>>> Simulation using LTSpice confirms that the 2N3904's actually saturate in
>>> this circuit.
>>> The phase noise performance will be poor.
>>> The transistor conduction angle is also poorly defined and significant
>>> conduction overlap due to saturation may render the circuit ineffective at
>>> high frequencies.
>>>
>>> The attached circuit schematic using a 1:4 (impedance ratio) input
>>> transformer will work much better and has a relatively well defined large
>>> signal input impedance.
>>> The output filter can be elaborated by replacing the 80pF caps with a
>>> combination of series tuned LC traps and a smaller shunt capacitance to
>>> reduce the level unwanted components.
>>> Suitable 100uH inductors (with SRF>  20MHz) are readily available from
>>> Farnell/element14.
>>> The output impedance is relatively low and a better match to 50 ohms may
>>> be achieved by adding a suitable low phase noise output buffer amp stage.
>>> Alternatively a 4:1 impedance ratio transformer can be used at the
>>> collector node with its primary shunted by a 200 ohm resistor.
>>>
>>> Any balancing circuitry (should this be necessary) should be implemented
>>> at the BJT emitters as any attempt to do this at the collectors will be
>>> ineffective.
>>>
>>> Bruce
>>>
>>> Bruce Griffiths wrote:
>>>        
>>>> Paramithiotti, Luciano Paolo S wrote:
>>>>          
>>>>>     http://www.timeok.it/files/5_to10_mhz_advanced_doubler.pdf
>>>>>
>>>>>            
>>>>>> This design appears to have gone somewhat astray.
>>>>>> high impedance unless of course the transistors enter saturation in
>>>>>> which case the phase noise performance will be severely degraded.
>>>>>> The best place for a balance adjustment circuit is actually in the
>>>>>> emitter circuit.
>>>>>>              
>>>>> *The collector balancing work correctly and is more simple to
>>>>>            
>>> implement.
>>>        
>>>>>            
>>>> I contend that the collector balancing technique you use only works
>>>> because the doubler isn't operating correctly.
>>>> With a high impedance collector output it would be relatively
>>>> ineffective unless the balancing resistance is increased to a level
>>>> that degrades the phase noise performance or saturation occurs.
>>>>          
>>>>>> The description of the biasing is misleading in that the actual bias
>>>>>> level that sets the crossover current is determined by the signal
>>>>>> dependent voltage>across the two 0.1uF capacitors in the emitter.
>>>>>> With a 1:1 input transformer the quoted figure of 35 ohms for the
>>>>>> input impedance seems excessive for large signal operation of the CB
>>>>>> stages unless of>course they saturate.
>>>>>>              
>>>>> *the input impedance is 35 Ohms @ 0dBm as measured with network
>>>>> vector analyzer. It can be upgraded to 50 ohms adding resistance on
>>>>> emitters, with some gain reduction and probably less phase noise. I
>>>>> will do some modification in the next future, including an input 6
>>>>> Mhz low pass filter. As you know, the input signal have to be pure
>>>>> sinewave to avoid unsymmetrical positive and negative half wave and
>>>>> obvious unbalaced output and high harmonics contens. I will test also
>>>>> the common emitter configuration to better isolate the doubler from
>>>>> the input impedance and level variations. Regarding the input level I
>>>>> have setup it's range, as my personal standard,from +7 to +13 dBm.
>>>>>
>>>>>            
>>>> I thought as much, the large signal input impedance (this is far more
>>>> important than the small signal value) will be much lower.
>>>> Since the bias shifts with input signal level the small signal input
>>>> impedance that you measured is of little value.
>>>>
>>>>          
>>>>>> It would also appear that the 20MHz tank 5.6uH + 12pF as drawn is
>>>>>> inappropriate in that it inevitably leads to saturated operation.
>>>>>> A series resonant 20MHz tank from the collector node to ground would
>>>>>> be a better choice.
>>>>>>              
>>>>> * The LC on collector is to adapt the impedance between the doubler
>>>>> and the filter and to cut the higher harmonics. The filter itself
>>>>> contain trap for 15 20 and 30 Mhz.
>>>>>
>>>>>            
>>>> Maybe so, but the filter input topology adopted is inappropriate for
>>>> low phase noise and avoiding saturation.
>>>> Attempting to match the (poorly predictable and varying - with
>>>> temperature and input signal level) collector output impedance to the
>>>> filter input impedance is misguided, just treat the output as a high
>>>> impedance source. The 4:1 (impedance ratio) output transformer should
>>>> suffice, if necessary you can add a 200 ohm resistor in shunt from the
>>>> collector node to Vcc if you need a 50 ohm output impedance. In
>>>> practice it may be better to buffer the output with a series
>>>> transformer feedback stage with well defined output impedance. Series
>>>> resonant LC traps from the doubler collector node to ground should be
>>>> more effective than parallel resonant series traps in that the high
>>>> frequency component amplitudes at the doubler collector will be
>>>> significantly reduced rather than enhanced by the filter.
>>>>
>>>>          
>>>>>> A snapshot or even a sketch of the collector voltage waveforms would
>>>>>> be useful in showing that the transistors saturate or not.
>>>>>>              
>>>>> *Actually the prototype is gone to friend's home and I cannot do any
>>>>> more measure on it. My next prototype's pubblication will be complete
>>>>> of collector voltage waveform to better understand the working
>>>>> condition of the doubler stage. I think the 2N3904 is not the best
>>>>> solution, i will test some more devices and bias point.
>>>>>
>>>>>            
>>>> At 10MHz you will find that most wideband transistors will be noisier.
>>>> However using transistors with a lower base spreading resistance than
>>>> the 2N3904 may be useful.
>>>>          
>>>>> Thank you
>>>>> Luciano
>>>>>
>>>>> note: I'm not a genius, I just try to enjoy myself. If someone follow
>>>>> me, is at his own risk.
>>>>>
>>>>>
>>>>>
>>>>> Luciano P. S. Paramithiotti
>>>>>
>>>>>
>>>>>            
>>>> Bruce
>>>>
>>>>
>>>> _______________________________________________
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>>>>
>>>>          
>>>
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>>
>>      
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