MONOCOIL SUCCESS

[mickstv]

I reckon just make up a diff amp using ne5534 ... ???

moodz

Got plenty of them. I also have a INA133UA sitting in the parts bin, unity gain diff amp. Might be ideal if it doesn't have input diodes.

http://www.ti.com/lit/gpn/ina133

Mick

[moodz]

I guess it will be time to look for a replacement, any ideas ?



Mick

I reckon just make up a diff amp using ne5534 ... ???

moodz

[moodz]

No worries moodz, I understand it's busy time of year.

Thanks mick, look forward to seeing your results.

I'm going to be using the lme49990 mainly because I read they were about the best available for a traditional design in a thread somewhere on here, so I'd already purchased a bunch. Seems quite a bit better than the THAT to me. Significantly better CMRR (137db), slightly lower noise, good bandwidth. Pretty old thread so I've got no idea if its the ducks nuts any more, technology marches on and all, so probably not.

Cheers Midas .... I will get some results but Mick will probably beat me to it. The LME49990 certainly has some pretty good looking specs but it is an OP-AMP not a diff AMP like the THAT .... snippet from the 49990 spec sheet below if you want a diff amp ... I am not saying dont use it though ...( if you got em ... smoke em )

moodz

[Midas]

No worries moodz, I understand it's busy time of year.

Thanks mick, look forward to seeing your results.

I'm going to be using the lme49990 mainly because I read they were about the best available for a traditional design in a thread somewhere on here, so I'd already purchased a bunch. Seems quite a bit better than the THAT to me. Significantly better CMRR (137db), slightly lower noise, good bandwidth. Pretty old thread so I've got no idea if its the ducks nuts any more, technology marches on and all, so probably not.

[mickstv]

Mick .. you probably already know but there are protective diodes on the inputs of the THAT if the input voltage to the amp exceeds the amplifier power supply the diodes will conduct ... this could also upset the blocker .... you should maybe consider using a series resistor of upto 10k on each input to the amp to limit any current flows if something bad happens. This will marginally degrade the noise performance but will save the amp.

moodz

I guess it will be time to look for a replacement, any ideas ?



Mick

[moodz]

Sure will, money doesn't grow on trees. I've got a couple of STP9NK50ZFP mosfets that I will try, looking at the specs it has a lower capacitance than the IRF740.



Mick

Mick .. you probably already know but there are protective diodes on the inputs of the THAT if the input voltage to the amp exceeds the amplifier power supply the diodes will conduct ... this could also upset the blocker .... you should maybe consider using a series resistor of upto 10k on each input to the amp to limit any current flows if something bad happens. This will marginally degrade the noise performance but will save the amp.

moodz

[mickstv]

That would be good ... just make sure you check the blocker is working or you know what will happen to the amp

moodz

Sure will, money doesn't grow on trees. I've got a couple of STP9NK50ZFP mosfets that I will try, looking at the specs it has a lower capacitance than the IRF740.



Mick

[moodz]

Hi Moodz, I should have a chance in the next day to two to try this front end, I'll post up the in air results on the .4gram nugget I have.

I take it I can still use the THAT1510 as the preamp.




Mick

That would be good ... just make sure you check the blocker is working or you know what will happen to the amp

moodz

[mickstv]

Hi Midas and thanks .. I am caught up with end of year stuff at the moment ... the aim of this circuit is mainly to reduce EMI ... the faster sampling was a surprise. I would assume that if the noise is removed then the sensitivity can be increased and thus smaller targets.
I will have hook up the amp and demod.

moodz

Hi Moodz, I should have a chance in the next day to two to try this front end, I'll post up the in air results on the .4gram nugget I have.

I take it I can still use the THAT1510 as the preamp.




Mick

[moodz]

Thanks Moodz, looks awesome. Not to be greedy but is there any chance you could post some target scope shots to get an idea how well this actually works? Ideally uber small gold since that seems to be the main reason people strive for superfast sampling, but hey whatever you have handy would still be interesting.

Hi Midas and thanks .. I am caught up with end of year stuff at the moment ... the aim of this circuit is mainly to reduce EMI ... the faster sampling was a surprise. I would assume that if the noise is removed then the sensitivity can be increased and thus smaller targets.
I will have hook up the amp and demod.

moodz

[Midas]

Target shots! Ra! Ra! Ra! Ra!

Thanks Moodz, looks awesome. Not to be greedy but is there any chance you could post some target scope shots to get an idea how well this actually works? Ideally uber small gold since that seems to be the main reason people strive for superfast sampling, but hey whatever you have handy would still be interesting.

[Aziz]

Aziz ... are you sure your library models are working OK ..... add on libraries sometimes dont work because they dont model underlying ideal device behaviour correctly.

Anyway here is the file ... make sure you run the sim till the voltage reachs 16 volts on C1 ( stable operating condition ).

Dont forget .. I ran this on the "real" simulator .... using real parts in a real circuit

moodz

[ATTACH]17711[/ATTACH]

Hi moodz,

ok, I have ran the sim much longer so the gate voltage stabilizes at 16 V. In this case, it works.
But the blocking fet circuit needs further improvements.

Aziz

[6666]

Thanks Mr Moodz
this is great info
cheers
6666

[moodz]

just to be clear ....

Output of blocker and TX gate pulse

The Simulation result .....


And the result using real devices ( IRF740 etc etc )

[moodz]

Hi moodz, do you need to change something in code or last version is applicable here too?

WM6 are you talking about the UNIPI code for the control chip ?? I did not change the code.

But I did try differenty types of Mosfets in the circuit and they all work ... they just have different maximum break down voltages.

The highest breakdown reached 1700 volts but this is not practical.

moodz.