analog multiplier help

Have a look at the Burr-Brown - now TI - MPY634, which is claimed to make 10MHz.

And I'm surprised that you have missed the very simiar Analog Devices AD734

--------------- Bill Sloman, Nijmegen

I'm looking for an "mixer" circuit to detect a sine waves DC to 10MHz,

3Vp-p max, and use IF output of 5kHz. Both the LO and the signal inputs are generated by DDSs. If large harmonics are present on the LO then there is good possibility they will mix with non-harmonic spurs generated by the signal DDS. RF mixers are generally square wave LO driven (or sine waves that fully switch long tail pair transistors) and therefore will generate lots of harmonics. This is the reason an analog multiplier is in my mind. LO 3rd harmonic of -40dB is low enough.

Currently manufactured multiplier ICs I have found:

AD835 (expensive, easy to use) AD633 (cost ok, but only 1MHz) HA2556 (price ?, difficult to buy)

I looked at a discrete design with total of 19 NPN transistors + 1 op-amp. (see schematic

)

SPice simulation of perfectly matched transistors gives great results on screen, but I'm very unsure what will happen in practice. Voltage offsets at each input will cause carrier feedthrough, but these can be trimmed out with yet more components. Neither power consumption or supply voltages are a concern.

Apart from the high part count is there any major problems with going for a discrete analog multiplier ?

Bill Sloman pointed out the AD734, which I believe does 10MHz.

The biggest issue with a discrete design (aside from power and size) is likely to be caused by device matching. These Gilbert-cell things work miracles, but are incredibly sensitive to DC parameters. Area mismatch of the core devices will give rise to second harmonics, which might be a problem in your system. This is easily trimmed out but adds still more complexity.

In a recent IC I designed I used some simple Gilbert multipliers and found that even a 0.5% mismatch produced unacceptable results, requiring trims. And this was in an IC, where all the transistors are close together and nominally "identical". It can only be worse in a discrete design where two parts from the same bag could come from very different sections of the same wafer, or even different wafers, won't necessarily be running at the same temperature, etc.

I think you'll have far fewer headaches if you go with the IC. Both ADI (disclaimer - I work for them) and TI offer parts suitable for your needs.

HTH

Steve

email address is nonfunctional, please reply to group

Hello Bill,

But be prepared to shell out more than 10 bucks a pop.

Regards, Joerg

I agree. I also recommend the AD734, despite its $22 cost. Adam S can fill out Analog's form and get two free samples.

--
 Thanks,
    - Win

Barry Gilbert of Analog Devices has published a number of papers on "Gilbert cell" mixer's and multipliers.

A search on "Gilbert B." + translinear on scholar.google.com picks up some 28 references.

You should be able to get pretty fair idea of what goes into the Analog Devices mulitpliers if you read a few of them. More than enough to make you feel comfortable, in my expereience.

------------------ Bill Sloman, Nijmegen

can you give us more info about your application and why you are concerned about LO harmonics...

square wave LO drive usually improves the linearity of a mixer...

Mark

With an integrated product you don't know whats in there and normally that makes me feel uncomfortable. OK you can check the data sheets but still I would go the harder and more challenging way. Instead of worrying about matching 9 or 16 transistors why not adopt the simpler way used in the older radios of single active devices.The performance wasn't/isn't bad. Some used dual gate Mosfets as mixers . With a dual gate config. you get amplification of 2 inputs in a single stage instead of building seperate single arrays for amplification. The input from the LCO is mixed with that of your RF input and output is an amplified mixture of the product. Besides BJT mixers give a somewhat linear response to the input versus the better square law characteristic of the MOS. You could still go for a much simpler single BJT mixer but for the reasons above, lower intermodulation distortion easier biasing, lower harmonic content, higher p-p voltage swing etc I'd go for a MOS/FET.

"Go easy on the whisky"

theJackal

For what frequencies?

Such as?

My impression is that the virtues of dual gate MOSFET mixers have everything to do with the good behaviour of the components at relatively high frequencies.

The OP wants good mixing - and explicityl wants to minimise spurious high order product spurs - at frequencies up to 10MHz, A well compensated Gilbert cell multiplier will do much better than a MOSFET for this sort of job. He also wants to use fairly high level signals, which won't work well with a dual -gate MOSFET mixer.

The numbers for the MOSFET would have come from "Transistor Circuits and Applications" (Prentice-Hall series in electronic technology) by Laurence G Cowles ISBN: 0139300732.

The ISBN is for the second edition from 1974 - I had the first edition, until it got soaked when a pipe froze in Cambridge U.K. some twenty years ago.

------------- Bill Sloman, Nijmegen

Can you still open the pages? Anyway, yes, bipolar transistors in a balanced Gilbert cell should do far better than a JFET or MOSFET mixer any day, thanks to the BJT's higher transconductance at any given operating current. First, the BJT's higher transconductance acts to reduce the effects of DC imbalance, and second, the BJT's intrinsic DC offsets are much lower than for JFETs or MOSFETs. (A caveat must be introduced for high background-noise levels.)

We should point out an excellent high-frequency bipolar Gilbert cell IC available from Intersil, the HFA3101. The hfa3101 uses 10GHz transistors (10-50mA) that can be used at reduced currents like 2 to 5mA, and still yield a superior performance at 10MHz.

and DigiKey stocks the HFA3101B version at $4.28 each, or $2.48 qty 100. Newark has them too, same price singles, but charges $3.65 qty 100.

The HFA3102 is also a useful part, among others in the UHF series.

--
 Thanks,
    - Win

Thanks, but I noticed the price is getting kind of steep. The AD835 is accurate enough for me and is 1/2 price of the AD734. The old Motorola MC1495 would be perfect, but this device was made obsolete sometime in the 1990s. Since this is for a low volume application, and the warnings I get from Stephan Goldstein, I think shelling out money for an IC is a better option. I could waste a week fiddling around with a discrete design only to find it with high levels of untrimmable distortion. The "signal" input to a Gilbert cell is typically at the lower differential transistor pair (Q6/Q9 in

)

Provided Re of these two transistors is low relative to the emitter degenerative resistor , R4, then distortion will be minimal. The "LO" input port however must go through a linear->non-linear then non-linear->linear translation, comprised of Q2/Q3 and Q5/Q7/Q8/Q9. This input port will naturally give higher distortion and is probably the reason why 4 quadrant multiplier ICs specify one input with greater linearity than the other.

Adam

Ummm.... Reasons why I prefer discrete components.

1) A designer should be familiar with discrete circuit disegn techniques , something he/she loses when using integrated circuits. 2)You compromise circuit flexibility when you use an integrated circuit 3)Discrete communication circuits are superior to integrated circuits in performance.

Your Proof? I disagree. Its a well known fact that MOS/FET are superior to BJT mixers. Try reading something on that.

"Go easy on the whisky"

theJackal

But since this is multiplying by a square wave, it adds in the products corresponding to all the odd harmonics of the fundamental frequency of the LO drive - albeit with excellent linearity.

Someone who wants to cover a large range of frequencies might find it inconvenient to have to filter them out.

----------------------- Bill Sloman, Nijmegen

Experienced analog engineers will recognize the hfa3101 and 3102 part numbers from the CA3101 and '02 parts introduced by RCA in the early days of linear ICs. RCA introduced a line of transistor array ICs that gave analog designers access to powerful matched- transistor design techniques, routinely used by IC designers, but otherwise not available to the rest of us. For example, the ca3045, ca3046 and ca3086 were five-transistor NPN arrays, and the ca3096 was an NPN + PNP array with five "high-voltage" 35V transistors. NSC chipped in with the LM3046, pardon the pun.

As the years went by, GE, RCA and Intersil became owned by Harris, who eventually tired of them, and spun them off as Intersil.

Sadly, most of the old high-voltage (e.g. 15V) arrays have been discontinued, but a few, like the ca3083, ca3086 and the ca3127 (with 1GHz transistors) have remained, although distributors may not carry them. The LM3046 is still available, but only in SMD.

In place of the lost "high-voltage" arrays we've gotten a few newer "low-voltage" parts having the same schematic and pinout, but made with much faster transistors. The original parts had through-hole DIP packages, well suited for experimenters, but the new parts are SMD only.

Here's a little table of the array's NPN transistor properties to jog our memories, and a comparison to the newer parts.

NPN ca3046 spec ca3086 ca3083 ca3096 ca3127 hfa3127 ---- ------ ------ ------ ------ ------- DIP? X X X X soic only Vceo 15 15 35 15 8 V IC-max 50 100 50 20 65 mA beta 100 70 390 85 130 f_T 550 450 335 1100 8000 MHz C_cb 0.58 - 2.25 0.2 0.6 pF (0.3 on die) C_sub 2.8 - 3.0 1.3 - Intersil also offers the hfa3134 and hfa3135, which are NPN and PNP matched pairs with f_T = 8.5 and 7GHz.

--
 Thanks,
    - Win

Hello Adam , What exact part number do you need? I will get you a price. Thanks Mike snipped-for-privacy@otxi.com

Adam S wrote:

And he won't be much interersted in mixer performance in situations where all of the frequencies being mixed are lower than 10MHz. Long wave and medium wave radio transmission is still of coomercial significance, but nobody write books about it any more.

They do - that is their particular virtue.

But not a low as a good analog multiplier in the frequency range where the analog multiplier is good.

But not analog multipliers - right?

And the analog multipliers like the AD734 are specified for +/-10V signals. This is a different ball-park.

He wanted a low frequency mixer, and you are giving him advice derived from microwave and broadcast journals. Win and I are coming out of the scientific instrument literature, where the OP's low frequency interests are much better represented.

------------------ Bill Sloman, Nijmegen

NEC has some nice multi-GHz duals and arrays.

John

Sure there is, and it's very big.

John

Thats totally OT. There is no DC imbalance in a dual gate MOSFET

That is unclear but as far as I know gm/I ratio is lower for a FET then a BJT.

"Go easy on the whisky"

theJackal