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Need help to design a transimpedance amplifier
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Hello ?guys..
I want to design a trans-impedance amplifier to detect currents of the APD (in the range of 200 nA to 100 micro A). Could some one suggest me the best IC with less bias current, single supply (+5 V only) and how to design a high sensitive TIA..? (typically, for every 100 nA change in the current, 100 mV voltage should be displayed). |
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¿ªÔÆÌåÓýYou have an impossible set of criteria for a linear TIA. You ask for 100mV per 100nA. 100uA is 1000 times larger than 100na. So, your spec would have 1000 times 100mV out with 100uA in, or 100V. You obviously cannot get that with a 5V only system! Your choices are to reduce sensitivity or use a logarithmic TIA circuit.Jim James Wagner Oregon Research Electronics
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Hello,?t.obulesu:
For log amp, there is a (TI) log112 model at the file folder, you could take reference of the following: ? It shows some .TRAN issues, if you could fix it, maybe you could feedback to the file folder.If you need really to implement one instance, there is a technique could average the background noise "white noise". It utilizes the op amp in voltage-follower (multiples in parallel) to averaging the noise (normally it's called "white noise"), it's not eliminated but averaged. It might be helpful. If you finally get helped from those techniques, feedback the forum, show how it take effect, lightly or significant. if so, everyone should appreciate you. Good day! Best regards. |
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That is quite easy. There lot of cmos type opamp with low drift spec. You can have t network on feedback which keep cost down for single opamp design. You also need cap on feedback to keep it stable. On 2 Aug 2016 20:24, "t.obulesu@... [LTspice]" <LTspice@...> wrote:
> > ? > > Hello ?guys.. > > I want to design a trans-impedance amplifier to detect currents of the APD (in the range of 200 nA to 100 micro A). > > Could some one suggest me the best IC with less bias current, single supply (+5 V only) and how to design a high sensitive TIA..? (typically, for every 100 nA change in the current, 100 mV voltage should be displayed). > > > |
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To?t.obulesu: I think you don't have a good understanding of the problem you are trying to solve.? You asked this question twice already.? You got an answer before too, which you apparently ignored.? I get the feeling you do not understand what the constraints and the requirements are.? Your expectations are unrealistic. FYI, this is not a place to help you design your circuit.? We can help with the simulations, once you have a circuit. Regards, Andy |
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¿ªÔÆÌåÓýUnlike a conventional op-amp circuit, the capacitance at the summing junction is extraordinarily important for bandwidth and stability. You can discover this through simulation. Likewise, you can use simulation to explore the requirements for gain-bandwidth product and such. Be aware that often, secondary parameters such as input capacitance are NOT included in simulation models unless the model uses actual transistors for the input stage rather than just a behavioral model.Jim James Wagner Oregon Research Electronics
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Let me say why am looking for new design..
We are currently using the receiver module which has three stages: 1. Trans Impedance stage 2. High Pass filter (HPF) stage 3. Unity gain amplifier (just for inverting the output of the HPF) Well...we used LM2662 as a -5V supply.. Here on we could see the hell noise below 100kHz.. I couldn't get rid of this noise by using bypass caps..but I could just reduced it.. Yet there is a lot of noise all across the circuit ranging from few kHz to hundreds of MHz... are the links where I have uploaded couple of documents.. I really don't know what sort of noise it is and from where it is coming... |
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John Woodgate
¿ªÔÆÌåÓýDON'T upload stuff anywhere but to the list web site. You can upload any sort of file to Files => Temp but big graphics files can go to Files => Big Files. ? With best wishes DESIGN IT IN! OOO ¨C Own Opinions Only J M Woodgate and Associates Rayleigh England ? Sylvae in aeternum manent. ? From: LTspice@... [mailto:LTspice@...]
Sent: Thursday, August 4, 2016 8:32 AM To: LTspice@... Subject: [LTspice] Re: Need help to design a transimpedance amplifier ? ? Let me say why am looking for new design.. |
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¿ªÔÆÌåÓýCheck the datasheet for the OPA 2846: Vn=1.2nV/sqrtHz, In=2.8pA/sqrtHz that means the OSI (optimum source impedance) is 428 ohms. The 100k resistors in the non-inverting inputs alone introduce 88uV (@100kHz BW) What is the transducer's impedance? Le 04/08/2016 ¨¤ 09:31,
t.obulesu@... [LTspice] a ¨¦crit?:
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Hi.
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The author of this opus (-Building of an optical lever system(1).pdf) or illiterate, or not very neat. Two schemes contain errors. While it may be disinformation. Bordodynov. 04.08.2016, 11:58, "t.obulesu@... [LTspice]" <ltspice@...>: Yahoo! Groups |
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Am 04 Aug 2016 00:31:30 -0700
schrieb "t.obulesu@... [LTspice]" <LTspice@...>: Let me say why am looking for new design..Hello t.obulesu, this is not the forum to discuss your circuit. Nevertheless, I'm stumbled about the following things, that might give you a hint you could thing about: Interpreting the image tek0000.png (red curve FFT) and in case I'm right, I can see a carrier at about 2.75Mhz with a spectrum of about n times ~300kHz width. This carrier may come from the SPI clock frequency. Furthermore I guess, the 300kHz might come via GND or VCC from the internal DAC oscillators, specified in the range from 250 to 340 kHz in the datasheet. Then, grounded on the fact, that the oscillators of the two DACs are not synchronised, their difference frequency is down-converted and will result as "noise" in the low kHz range. Check your PCB layout with respect to crosstalk paths and GND loops. Sorry for my broken English. -- Mit freundlichen Gr¨¹?en Kind Regards Peter Ragosch peter.ragosch@... |
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This is the case when first creating a source of noise, and then heroically fighting with them.
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It is better not to use a charge pump to get negative voltage. You can build tranimpedansny amplifier of three transistors: common collector (npn), Common emitter (npn) and common collector (pnp). Three resistor and feedback resistor. Bordodynov. 04.08.2016, 13:46, "t.obulesu@... [LTspice]" <ltspice@...>: I have uploaded them with the name..New Microsoft PowerPoint Presentation(2).pdf and Noise.pdf here in files.. |
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¿ªÔÆÌåÓýI tried to answer a couple of days ago, but it didn't come through, so I'll write it again: The noise you observe compes from the fact that you have these
big 100k resistors in the non-inverting inputs. The OPA2846 has a
very high NOISE CURRENT; it is designed for low-impedance sources.
There should be no resistor in the non-inverting inputs, or very
low (similar to the APD's equivalent resistance); if used, this
resistor should be bypassed by a capacitor, for near-zero
impedance within the circuit's BW. That's VLN 101. Le 04/08/2016 ¨¤ 09:31,
t.obulesu@... [LTspice] a ¨¦crit?:
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I design a lot of TIA type of amp. I don't know what kind of speed you are looking for. But your requirement is very easy, the lowest is 200nA. Any opamp with bias current of less than 10nA will work good enough.
I use LTC6268 for my design. It is likely to be way over kill for you. Check out other opamp from LT. A tip for you, I tested out a lot of opamps from Ti and Maxim. Most don't quite meet the spec on the noise even the spec say so. LT6268 really produce the result according to the spec. Contact Glen Brisebois in LT linear opamp application group. He is very knowledgeable and helpful. I visited him in the head quarters once and he showed me a lot of tricks. |
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