emi hardened opamps

Another quick and dirty but very effective test method is to hold the antenna of a GSM mobile phone over each part of the circuit in turn. Only the first few seconds of each test call should be used because after that the dynamic power control may reduce the signal level.

For lower frequencies a dual-band VHF/UHF DMR digital walkie-talkie is useful. These are now available fairly cheaply from China. Make sure that you choose one that supports dual timeslot repeater operation as some of them cheat and radiate continuously rather than pulsing the carrier on and off at 16.666Hz. Some of these radios are now available with 10W output power at VHF and 8W at UHF. You can get a business radio license (in the UK at least) that makes it legal to radiate at selected VHF and UHF frequencies. The new Ailunce HD1 looks easier to configure from the handset for such tests than most of the others. I have not tried one of these (yet) and have no connection with Retevis who make it. However, I am planning to get one for this purpose.

John

Reply to
jrwalliker
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Here is my VME EMI MasterBlaster board. We can use this to pump RF onto zones on either side of the VME board that I'm having EMI troubles with. We might drive it from a fast pulse generator, or from an RF signal generator. I'd expect to find fairly narrowband resonances on the victim board.

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No, it's not some precision matched-impedance antenna thing. If I get ambitious I guess I could replace the long runs with hardlines.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Fat chance. It's still bipolar.

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Bill Sloman, Sydney
Reply to
bill.sloman

To get those low offset voltages in OP-27s and such they used tricks that make a front end very non-linear. I had nothing but trouble using them in the RF rich environment of a fusion energy experiment. Filtering worked, but expensive.

Paul Probert

Reply to
electrogas

John,

I just happened across this one:

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36V supplies, 1.1nV/rtHz, 125uV offset.

It specs about 30dB of EMI rejection at lowish R.F.

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Cheers, James Arthur

Reply to
dagmargoodboat

John Larkin wrote:

Keep your op amps, add a proper filter. 5 stages gives 75pf input capacity,

5k series resistance, -3dB at 900KHz, -100dB at 100MHz.

Adding a 6th stage doesn't do much.

Version 4 SHEET 1 1416 680 WIRE 432 -160 416 -160 WIRE 464 -160 432 -160 WIRE 576 -160 544 -160 WIRE 624 -160 576 -160 WIRE 720 -160 704 -160 WIRE 768 -160 720 -160 WIRE 800 -160 768 -160 WIRE 896 -160 880 -160 WIRE 944 -160 896 -160 WIRE 976 -160 944 -160 WIRE 1088 -160 1056 -160 WIRE 1136 -160 1088 -160 WIRE 1152 -160 1136 -160 WIRE 1248 -160 1232 -160 WIRE 1296 -160 1248 -160 WIRE 1312 -160 1296 -160 WIRE 576 -144 576 -160 WIRE 720 -144 720 -160 WIRE 896 -144 896 -160 WIRE 1088 -144 1088 -160 WIRE 1248 -144 1248 -160 WIRE 416 -128 416 -160 WIRE 576 -64 576 -80 WIRE 720 -64 720 -80 WIRE 896 -64 896 -80 WIRE 1088 -64 1088 -80 WIRE 1248 -64 1248 -80 WIRE 416 -32 416 -48 FLAG 432 -160 Vin FLAG 576 -64 0 FLAG 768 -160 R2C2 FLAG 720 -64 0 FLAG 576 -160 R1R2 FLAG 416 -32 0 FLAG 944 -160 R3C3 FLAG 896 -64 0 FLAG 1136 -160 R4C4 FLAG 1088 -64 0 FLAG 1296 -160 R5C5 FLAG 1248 -64 0 SYMBOL res 560 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL cap 560 -144 R0 SYMATTR InstName C1 SYMATTR Value 15p SYMBOL res 720 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL cap 704 -144 R0 SYMATTR InstName C2 SYMATTR Value 15p SYMBOL voltage 416 -144 R0 WINDOW 123 37 69 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 25 97 Left 2 SYMATTR Value2 AC 1 SYMATTR Value PULSE(0 1 0 100p 100p 1n 400n) SYMATTR InstName V1 SYMBOL res 896 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL cap 880 -144 R0 SYMATTR InstName C3 SYMATTR Value 15p SYMBOL res 1072 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL cap 1072 -144 R0 SYMATTR InstName C4 SYMATTR Value 15p SYMBOL res 1248 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL cap 1232 -144 R0 SYMATTR InstName C5 SYMATTR Value 15p TEXT 608 -360 Left 2 !.ac oct 1000 10k 1e8 TEXT 600 -408 Left 2 ;'Five Stage RC Lowpass Filter TEXT 1048 -368 Left 2 !.options plotwinsize=0 TEXT 1048 -344 Left 2 !.options numdgt=15 TEXT 608 -336 Left 2 ;.tran 1u TEXT 608 -312 Left 2 ;.ac oct 1000 10k 1e8

Reply to
Steve Wilson

It's got a bipolar input. FET input op amps do better when the problem comes from higher RF frequency interference - above the bandwidth of the op amp.

The OPA192 that George recommended

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does offer a FET input.

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Bill Sloman, Sydney
Reply to
bill.sloman

Pricey!

Reply to
krw

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