little photo diodes and an opamp?

Started by George Herold in sci.electronics.design3 years ago 16 replies

The project seems to call for the smallest detectors. I'm buying a few each of 'all'* the little PD's from digikey. (I can share a list if...

The project seems to call for the smallest detectors. I'm buying a few each of 'all'* the little PD's from digikey. (I can share a list if someone wants... it's a mix of TH and SMD.) C_in between 1-3 pf when reversed biased. I don't see how it makes sense to bootstrap or cascode the PD**. So I was looking at opamps with small C-in. (Big thanks to H&H of AoE as always.) I've now g...


LT Spice powering opamps

Started by John Larkin in sci.electronics.design7 years ago 5 replies

I usually have a couple of "voltage" things off to the side, making +5 and -5 or whatever, and have each opamp with little doglegs on...

I usually have a couple of "voltage" things off to the side, making +5 and -5 or whatever, and have each opamp with little doglegs on its power pins, same net names. Somewhere I thought I saw a circuit where the opamps were powered by little boxes with "+5" or something inside, with no other supply needed. Does that work? If so, how do you invoke it? -- John Larkin ...


Datasheet Jargon Translation Required

Started by Cursitor Doom in sci.electronics.design1 year ago 101 replies

Can some kind sould tell me what the following load of old cobblers from the datasheet of a FET opamp means in plain...

Can some kind sould tell me what the following load of old cobblers from the datasheet of a FET opamp means in plain English? ******************************************************************************** "As with most amplifiers,care should be taken with lead dress,component placement and supply decoupling in order to ensure stability.For example,resistors from the output to an input ...


TI opamp

Started by John Larkin in sci.electronics.design8 years ago 46 replies

Has anybody used this one? http://www.ti.com/product/lme49990 Sounds too good to be true. -- John Larkin Highland...

Has anybody used this one? http://www.ti.com/product/lme49990 Sounds too good to be true. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com


1/x function with op amps or multiplier or something else...

Started by Fibo in sci.electronics.design7 years ago 58 replies

Hello, I'm trying to figure out the best way to go about making a -1/x function in hardware. From googling around I see 2 methods, 1....

Hello, I'm trying to figure out the best way to go about making a -1/x function in hardware. From googling around I see 2 methods, 1. Inverting log -> Anti-log 2. OpAmp with multiplier in the feedback loop I have +/-5V rails available, and my input is from 0.4V to 2V (which should give me an output of (-2.5 to -0.5). All DC values. Can anyone point me in the right direction here, I'm


op-amp circuit wont work

Started by panfilero in sci.electronics.design11 years ago 38 replies

can anyone tell what I did wrong here? my goal is to measure current using an opamp, I need to be able to measure positive and...

can anyone tell what I did wrong here? my goal is to measure current using an opamp, I need to be able to measure positive and negative current, and I have these LTC2053 OpAmps available, but I'm trying to simulate what I'm thinking about doing in LTspice and I can't get any output at all.... I need to be able to see from 50uA to .1mA, which is a pretty big range (and I need this in positive...


Cap Multiplier, NOT a "gimmick"

Started by Jim Thompson in sci.electronics.design9 years ago 13 replies

Here's a way to do capacitor multiplication... limited only by OpAmp GBW product, and no resistive components until the OpAmps run out...

Here's a way to do capacitor multiplication... limited only by OpAmp GBW product, and no resistive components until the OpAmps run out of steam. Mathematically, this is the same way I did behavioral models for crummy capacitors such as X7R and Y5U, except I had ideal amplifiers, and equations and/or tables to des


lm358-like opamps

Started by Bill Martin in sci.electronics.design11 years ago 12 replies

Hi, anyone have a favorite brand/flavor of lm358 or equivalent opamp to recommend for a simple, low performance integrator to generate a...

Hi, anyone have a favorite brand/flavor of lm358 or equivalent opamp to recommend for a simple, low performance integrator to generate a voltage ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to two seconds duration, no repeating..one shot style. Looking at just Mouser, there seem to be 23 parts in soic-8 to choose from... Thanks, Bill Martin


Never Buy Maxim (again)

Started by John Larkin in sci.electronics.design9 years ago 130 replies

Maxim makes an opamp, MAX44280, that has a specified input capacitance of 0.4 pF. That would be great in some apps where Cin causes...

Maxim makes an opamp, MAX44280, that has a specified input capacitance of 0.4 pF. That would be great in some apps where Cin causes noise-gain peaking. I figured I'd give Maxim another chance, after being s*****d by them in the past. So I went online and filled out their sample request. The process makes no sense, website runaround, but eventually I got it done. Two days later I go...


speaking of substrate diodes...

Started by Anonymous in sci.electronics.design1 year ago 2 replies

leads to this one... https://www.dropbox.com/s/cgaxalnn3hhf315/RRIO_Logamp.jpg?raw=1 where we use the substrate diode of a RRIO opamp as a...

leads to this one... https://www.dropbox.com/s/cgaxalnn3hhf315/RRIO_Logamp.jpg?raw=1 where we use the substrate diode of a RRIO opamp as a logarithmic current-to-voltage converter. There are better ways to do this, but maybe none so cute. -- Father Brown's figure remained quite dark and still; but in that instant he had lost his head. His head was always most valuable whe...


C-multiplier again

Started by John Larkin in sci.electronics.design13 years ago 137 replies

I need a super-low noise power supply. I have a 15 volt switching wall-wart input and want as close to 15 volts, regulated, as I can get;...

I need a super-low noise power supply. I have a 15 volt switching wall-wart input and want as close to 15 volts, regulated, as I can get; 14 would be nice, 13.5 is OK. The LDOs that I can find are all pretty noisy and have mediocre PSRR. So I thought about using a Phil Hobbs-ian c-multiplier transistor, an R-C lowpass and an emitter follower, with a slow opamp loop wrapped around i...


why do they do this?

Started by John Larkin in sci.electronics.design3 years ago 132 replies

ST makes a nice little LDO, super-low dropout with an aux Vbias supply. Saves me from rolling my own with an opamp and a mosfet. It's an...

ST makes a nice little LDO, super-low dropout with an aux Vbias supply. Saves me from rolling my own with an opamp and a mosfet. It's an ST1L08. So why is the data sheet file en.DM00123507.pdf ? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com


opa145

Started by George Herold in sci.electronics.design3 years ago 19 replies

Hi all, Well the opa124 is EOL, suggested replacement is opa145. http://www.ti.com/lit/ds/symlink/opa145.pdf Looks nice. Very low 1/f noise...

Hi all, Well the opa124 is EOL, suggested replacement is opa145. http://www.ti.com/lit/ds/symlink/opa145.pdf Looks nice. Very low 1/f noise corner. And then I got a little worried looking a figure 17, which shows voltage noise rising from 10k Hz on.. and then the graph ends at 100 kHz. Anyone looked at used this opamp? I'm going to order a few. Thx George H.


semiconductor drift

Started by John Larkin in sci.electronics.design8 years ago 52 replies

We have two 8-channel waveform generators that were shipped 4 months ago, and came back because the customer ordered too many or something. We...

We have two 8-channel waveform generators that were shipped 4 months ago, and came back because the customer ordered too many or something. We routinely test anything that comes back, before returning them or returning to stock. What's interesting is that all 16 channels have a negative DC offset. Each channel is a diff-current-output cmos DAC, an opamp diffamp, a passive LC filter, and ...


simple opamp amplifier circuit

Started by panfilero in sci.electronics.design10 years ago 23 replies

I'm simulating on LTSpice, a simple amplifier circuit with a 2.5V offset, but if I don't include a capacitor on my input my output hits the...

I'm simulating on LTSpice, a simple amplifier circuit with a 2.5V offset, but if I don't include a capacitor on my input my output hits the rails... why is this? The link shows what I'm doing in LTSpice thanks http://i555.photobucket.com/albums/jj477/panfilero/Capture-1.jpg


Howland current pump question

Started by bitrex in sci.electronics.design8 years ago 28 replies

Is it normal for the op amp inputs of the Howland pump to not be at the same voltage? In all my experiments in LTSPICE with the "improved"...

Is it normal for the op amp inputs of the Howland pump to not be at the same voltage? In all my experiments in LTSPICE with the "improved" topology and grounded resistive loads, this seems to have been the case. The circuit obviously has both positive and negative feedback, but if the opamp output is not railed then I assume the negative feedback must be "winning." But if this is ...


Spice Model for OpAmp Output Stage

Started by Jim Thompson in sci.electronics.design6 years ago 18 replies

...Jim Thompson -- | James E.Thompson | mens | | Analog...

...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Cont


Flyback vs half-bridge

Started by Phil Hobbs in sci.electronics.design9 years ago 160 replies

So, I'm goofing off playing with small switchers. (Well, not exactly goofing off, but there are somewhat more pressing tasks waiting....) As...

So, I'm goofing off playing with small switchers. (Well, not exactly goofing off, but there are somewhat more pressing tasks waiting....) As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a small half-bridge supply with positive and negative voltage doublers. I'm not that keen on it, because (a) it uses a fair number of parts for what it does, and (b) it has a nasty ins


Opamp frequency mixer

Started by bitrex in sci.electronics.design7 years ago 56 replies

So as a hobby project I'm thinking of building a tiny little theremin using some of those Soviet subminiature pentodes that are really cheap...

So as a hobby project I'm thinking of building a tiny little theremin using some of those Soviet subminiature pentodes that are really cheap on eBay. Unfortunately, it seems that the most complicated part of the project would be the frequency mixers, as I don't think they really made subminiature heptodes and a "proper" mixer would probably require two tubes. I'm thinking about going s...


HV control

Started by George Herold in sci.electronics.design5 years ago 66 replies

Hi all, another circuit fumble on my part. I copied this circuit fragment from whit3rd... part of thread is pasted in below. Here's the...

Hi all, another circuit fumble on my part. I copied this circuit fragment from whit3rd... part of thread is pasted in below. Here's the circuit I built. https://www.dropbox.com/s/skaspzjafoqmcfl/HV-control.JPG?dl=0 I ground the base of Q2 and added R3 so that it would start out with the HV turned off. D1 was added because I was worried about the zenering Q2's base. (opamp has...