spi RF attenuator

Well, I did find this...

It's sure easy to program.

hittite ?

-Lasse

Aeroflex and also general microwave (herley)

Those RF guys are always annoying.

This is rated DC to 4 GHz, but "DC blocking capacitors are required."

The RF ports say that DC voltage is present, but they don't say how much.

I once used a Hittite part, an absorbtive 8PST switch, that was rated DC to 4 GHz. Turned out they internally define "DC" as starting at 100 MHz.

Hell, you never said an IC chip. I was giving links to modules.

My jellybean SPI attenuator of choice is the Mini-Circuits DAT-15R5-SP+. As usual, it's specified to work down to DC as long as your definition of DC is 0V. :( Also as usual, the data sheet tells you nothing about how it actually works.

It'd be nice if someone built a digital pot like the AD5260 with response into the VHF range. I'm not sure why those have such a low 3 dB bandwidth.

-- john, KE5FX

;)

These RF bods can't be expected to use zero-ohm resistors like the rest of us.

I've recently started putting zero-ohm resistors between linear regulators and their output reservoir caps. One recent test board had all the inverse-parallel diodes in backwards, leading to putting +15.5 V on the MCU's VDD pin. Too bad, so sad.

The other good thing about that is that if the regulator has any stability issues (e.g. an LM1117 with a big polymer aluminum output cap) I can just put N milliohms in series and fix it.

In hand-wired protos, I always wire and test the supplies first, then finish up.

Cheers

Phil Hobbs

Nor can they be bothered to reveal the DC behavior of their parts.

I never put reverse diodes across voltage regulators, and haven't suffered.

I go try to remember to put 0R or milliohm resistors in series with regulators, so we can measure the currents. Sometimes it's good to know that stuff, like FPGA core power, for future reference.

I generally use tantalums on an 1117 output, voltage derated 2:1 or so. That seems to be very stable. We avoid wet aluminum lytics, because the ESR skyrockets below 0C.

Yeah, my protos sometimes include regulators, so that I don't need six bench supplies.

Yup. I've been using AlPo caps there lately, because it helps prevent low-frequency crosstalk between different things hung off the same supply rail.

My standard is a 16-19V laptop power brick, with LM78XXes and LM2594s applied as necessary.

Cheers

Phil Hobbs

p)

for protos and one-ofs i sue something like this:

hard to beat the price

-Lasse

That's because they left out the inductor. ;)

I've used similar things in the past. Most of the Chinese ones work okay if you derate them by a factor of 2 or 3 in current. (They always cheap out on the inductor like that.)

My stuff usually has a lot of sensitive analogue sections, so I use a lot of toroids, especially in protos.

Cheers

Phil Hobbs

Good grief, does no one at MiniCircuits proofread their data sheets? It's a mess.

The requirement that the inputs be AC coupled, or held at ground, and that the max input limit is -0.3 volts, is interesting. That conflicts with the 24 dBm rating. Typical RF specmanship.

I think most of those are CMOS string dac architectures, nice and linear and monotonic but fundamentally slow. An n-bit unit has 2^n resistors and switches.

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.5 V

cap)

yeh I wouldn't bet on 3A.

but you don't need much at 1MHz, a similar sized coilcraft of that value is rated for 5A

The markings on the diode on the ones I have leads to a datasheet that says 3A average

The IC is an MP1584, rated at 4A

So it doesn't look totally hopeless

-Lasse

Try Hittite, now owned by Analog Devices Mark

As I understand it, their main business is packaging other peoples' dies. So they may just post whatever specs they get from the OEM. Hardly anybody in the MMIC business publishes decent data sheets.

I wonder if there's a charge pump in there that they're not mentioning? It 's supposed to be CMOS, not GaAs, and I've never caught it making racket. One reason I like the DAT-15R5 is that it doesn't contribute any additive A M or PM noise beyond its own loss.

Now that I'm looking at it, the DAT-15R5-SP+ is NRND and the data sheet for their recommended replacement part has a rather interesting new graph. I used the old part in a box rated for +20 dBm max input from 0.5-30 MHz, and figure 1 for the new DAT-15R5A-SP+ says that it should more like +10 dBm n ear 1 MHz. That's much more specific (and disturbing) than the original DA T-15R5 data sheet, which just says "Input IP3 and P1dB degrades below 1 MHz ." So caveat emptor, I guess.

-- john, KE5FX

Peregrine. For example, the PE43703. Power handling goes down as the freq uency gets low. The negative charge pump can be bypassed, if you don't wan t the low level noise they make. The 50 mdB settling is much faster than G aAs because GaAs has "gate lag."

h goes to DC with better power handling than anything preceding it. It is a matter of time until we see that in DSAs.

Thanks. I'll check Peregrine.