CurtPalme.com Home Theater Forum

[seanoise]

hello, i have a question for you!
is it possible to change easily the AD835 op-amps on the 2035-02P VIM against the better AD834 op-amps?

[Nashou66]

[cmjohnson]

If you're adept at handling 8 pin SOIC surface mount devices, yes.

I was about to ask a related question: If one were to change out the 835s for the higher bandwidth 834s on a 02P board,
what else would be required in order to maintain the enhanced bandwidth all the way to the output jack?

I would guess that there's got to be more to doubling the bandwidth of the VIM chain than simply swapping out three chips.

Incidentally, Analog Devices puts the price of this chip into the generally 20 dollar per piece range, in quantity. It's not the cheapest
chip in the world. I'm not enthusiastic about putting 60 dollars into parts and getting no improvement out of it. I'd want reasonable
assurances that it would work right before buying those parts.


I think it's time to at least consider the options for bandwidth expansion in light of 3D Blu-Ray players coming to market. The bandwidth
requirements for dual channel 1080p at 48 Hz per channel are considerable but easily fit into a 500 MHz window. I figure that 3D via our
CRT projectors may well require us to plan for that kind of bandwidth and framerate requirements.

CJ

[Nashou66]

Chris read my post above yours.

Athanasios

[cmjohnson]

I guess I was writing my post while you were writing yours.


I have a 03P VIM but it's in my machine right now. Hard to get out. Impossible, actually, without dropping the machine off the ceiling.


I'd like to compare them side by side just for curiosity's sake.

CJ

[draganm]

[seanoise]

i think i understand. the additionally op-amp in the ad835 generates the voltage-output, and the 834 only produces an current-output.
so, i have another question. is it possible to change the ad835 on the 02p vim against the adl5391 (apart from the fact, that it has 16 connecors instead of 8)?
it is a voltage-output multiplier too, with a bandwidth of 2Ghz. it has an extra scaling input, but it is not necessary to use it i think...
so, would this be possible?

[Nashou66]

I do not think they will work, it has a different formula for the multiplier I think, and the internals work different.

AD835





ADL5391



Athanasios

[Nashou66]

Reading more on it it says it does not operate well when getting close to DC or Black id presume with out the help of another external chip. I am not 100% sure on how it all works but Mike Parker or TSE would know more about that chip as a replacement, so after reading more it might be possible with lots of other changes, Lets see if they chime in, i'll ad a link tot he Data sheet. Page 10 is of interest for the theory of operation.


http://www.analog.com/static/imported-files/data_sheets/ADL5391.pdf

Athanasios

[seanoise]

yes the formula is different...

ad835: W=XY + Z (X=X2 - X1 and Y=Y2 - Y1)

adl5391: W=alphaXY/1V +Z (X=Xpls - Xmns and Y=Ypls - Ymns)

BUT, 1V is a constant of 1 volt. and if you don't use the scaling input, alpha ist 1 too.
so the formula have to be the same: W=XY + Z.

and in the specifics of the adl5391 i found these text:
"In the past, analog multipliers, such as the AD835, were implemented almost exclusively with a Gilbert Cell topology or a close derivative. The inherently asymmetric signal paths for X and Y inevitably create amplitude and delay imbalances between X and Y. In the ADL5391, the novel multiplier core provides absolute symmetry between X and Y, minimizing scaling and phasing differences inherent in the Gilbert Cell."

maybe someone has tried it?!

[Nashou66]

Right but you need the output to be AC coupled where as the AD835 is not, simplifying use according to the data sheet.
the ADL chip needs AC coupling or the external chips that will go down to DC or the use of other chips.

Calibration

The dc offset of the ADL5391 is approximately 20 mV but changes over temperature and has variation from part to part (see Figure 4).
It is generally not of concern unless the ADL5391 is operated down to dc (close to the point X = 0 V or Y = 0 V), where 0 V is expected
on the output (W = 0 V). For example, when the ADL5391 is used as a VGA and a large amount of attenuation is needed, the maximum
attenuation is determined by the input dc offset. Applying the proper voltage on the Z input removes the W offset. Calibration can be
accomplished by making the appropriate cross plots and adjusting the Z input to remove the offset.
Additionally, gain scaling can be adjusted by applying a dc voltage to the GADJ pin, as shown in Figure 5.


BASIC CONNECTIONS

Multiplier Connections

The best ADL5391 performance is achieved when the X, Y, and Z inputs and W output are driven differentially; however, they
can be driven single-ended. Single-ended-to-differential transformations (or differential-to-single-ended transformations) can be
done using a balun or active components, such as the AD8313, the AD8132 (both with operation down to dc), or the AD8352 (for higher drive capability).
If using the ADL5391 single-ended without ac coupling capacitors, the reference voltage of 2.5 V needs to be taken into account. Voltages above 2.5 V
are positive voltages and voltages below 2.5 V are negative voltages. Care needs to be taken not to load the ADL5391 too heavily,
the maximum reference current available is 50 mA.


Athanasios

[seanoise]

of course these are 2 problems...
maybe the offset you can cancel with the settings in the projector menus!?
and the ac-coupling could realised by a fitting capacitor!?
i only wonder, anybody had tried it...
if i had a spare vim i would do i think!

so now the experts are like MP are questioned...

[dvh99]

is the ad834 a direct replacement for the ad835 or are resistor changes needed.
i read the ad834 requires 0.1% precision resistors.

[dvh99]

http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556859&k=ad834
only 900+ available for a reasonable price, farnell charges 50 euro a piece.

[dvh99]

oops i missed a post it isnt possible.
how about the board jarmo was working on?

[dvh99]

since there is no easy way getting the 834 to work i was thinking of the peaking circuit with the varicap from the link.
it does however say in the spec sheet it has a current amplifier build in but i am not sure this is what is needed.

http://www.analog.com/static/imported-files/data_sheets/AD834.pdf

http://nl.farnell.com/murata/tz03r200f169b00/capacitor-variable-4-2-to-20pf/dp/1685438

would these be allright?
anyone knows what value resistors to use?

[dvh99]

niktec has a 03p vim but asks 500usd.
is niktec someone on this forum?

is it possible to use the peaking circuit on a 03p vim to get a bandwidth good for 350mhz.

[Sparky015]

Niktec I don't believe is on the forum, as they are a large company in Cincinnati OH, but they do know what they have and charge a fairly hefty price. I think someone sold an 03P VIM earlier this year in the $350 range. I would contact them and haggle on the price, They sometimes wiggle a bit.

[AnalogRocks]

Heads up guys Mike Parker has an 03 vim for sale: http://www.curtpalme.com/forum/viewtopic.php?p=260956#260956

[AnalogRocks]

Heads up guys Mike Parker has an 03 vim for sale: http://www.curtpalme.com/forum/viewtopic.php?p=260956#260956

[Sparky015]

ah, there you go. I would get Mike's and see if he would be willing to turn it into a super 03 VIM. Now that would be the poop!