| Electronics > Projects, Designs, and Technical Stuff |
| Looking for a low noise amplifier (<1nV / rt. Hz) |
| (1/4) > >> |
| jbb:
I’m working on a wide band current sense system (DC - 1MHz) and I’m hunting for a better amplifier. I checked Analog Devices (and this LT) and Texas Instruments and came up with the ADA4895-1, which will run off my +- 3.3V analog rails and has about 1nV/rt.Hz ven. The LT1028 is a tiny bit better but consumes a lot more current and needs +-5V rails. Can anyone suggest another supplier which might have something even better? |
| coppercone2:
I don't think you will get much better then those without parallel devices. |
| ejeffrey:
I have used the OPA211/OPA2211 which is 1.1 nV/rtHz and would work on +/- 3.3 V. At this level, remember that the noise density is usually specified at 1 kHz. If you want to compare 0.9 nV, 1.0 nV and 1.1 nV, you really need to look at the performance at the frequency you care about. This means including 1/f noise at low frequency and including the effect of input capacitance on noise gain at high frequency. Its really hard to do much better than 1 nV/rtHz, especially at low frequency. Some HEMT amplifiers do a factor of 2-3 better than that but only at high frequency, pretty much anything beyond that requires cryogenic cooling. Most current shunts are terribly matched to transistor amplifiers which have noise resistances in the hundreds or thousands of ohms. If you could live with AC coupling a transformer would really help. As an illustration, look at the SR554 which gets a noise voltage of 0.1 nV/rtHz by using a 100:1 transformer. |
| SiliconWizard:
Maybe the LT6200: 0.95nV/√Hz (100kHz) A lot more power hungry. ;D |
| jbb:
Thanks all I had a look at paralleling 2 op-amps, and it made some improvement (approx 20% drop in total system noise). I don’t think that’s worth it on my 1st prototype where I will likely have some other mistakes to fix. Thank you for mentioning the SR554, ejeffrey. Right now I’m looking for DC - 200 kHz (or 1 MHz) bandwidth, so a straight up transformer input won’t hit the spot. However, in version 2 or 3 I could have a look at a LF + HF path to get a wide band transformer in there. |
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