Newer Model Instrumentation Amp
in [Design]
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From: Paul Henderson on 20 Jun 2010 04:04 I have previously used AMP 01, INA114 and AD620 instrumentation amps for EEG apps. All maximum gain 10,000. Since these packages are all about ten years old now, I would like to update my design, if appropriate. Can someone advise regarding more recent and better spec'd IC's of this general type? Paul Hendersen
From: Stephan Goldstein on 20 Jun 2010 08:10 On Sun, 20 Jun 2010 08:04:52 GMT, paulhendersen(a)qualcomm.com (Paul Henderson) wrote: >I have previously used AMP 01, INA114 and AD620 instrumentation amps >for EEG apps. All maximum gain 10,000. > >Since these packages are all about ten years old now, I would like to >update my design, if appropriate. > >Can someone advise regarding more recent and better spec'd IC's of >this general type? > >Paul Hendersen Both Analog Devices and Linear Technology offer a variety of in-amps. I haven't kept up with ADI's latest offerings (I work for them, but in another area) but you might look at things with part numbers like AD86XX, these are newer devices. I don't follow LT as they don't compete with the stuff I work on. The parts you're familiar with may be in DIP packages - not many new parts are available in that type of package, surface mount has become the norm. Perhaps what you're using is available in SM, that form- factor will certainly have a longer production life than DIP. You might try that route first if your design is otherwise satisfactory. Always better to use something known to work than to try to "improve" it, that can often lead to unexpected adventures. Do you really need maximum gain of 10,000 for EEG? And when did Qualcomm get into the brains business? Steve Steve
From: Winfield Hill on 20 Jun 2010 08:38 Paul Henderson wrote... > > I have previously used AMP 01, INA114 and AD620 instrumentation amps > for EEG apps. All maximum gain 10,000. > > Since these packages are all about ten years old now, I would like to > update my design, if appropriate. > > Can someone advise regarding more recent and better spec'd IC's of > this general type? I recently finished updating our Selected Instrumentation Amps table for H&H AoE III. Except for low-voltage-process designs, I did not notice a lot of new activity in the last 15 years. Most of the classic parts are doing fine, especially if they're available in small SMT packages. Commenting on your choices, but for gains up to 1000 (most of the data sheets don't address G=10k, that's a lot in one stage). The AMP01 comes in a large awkward package, but it seems to do well at very high gains. However, it didn't make our list. I wasn't able to find distributor inventory. Lack of interest? The INA114 is rather slow at high gains, the INA128 has similar input characteristics, but is about 10x faster at high gains. Both are fine at distributors, maybe the INA128 has the edge. The AD620 is a respectable part, popular, inexpensive. But its 80dB CMRR at 10kHz pales compared to the INA128's 105dB. The AD8221 is similar to the AD620, cheap, with 87dB CMRR. The AD620 and AD8221 both let you directly bypass the input transistors for RFI suppression. The INA128 may as well, but TI hides the circuit details from the engineer. Too bad. You might want to consider some JFET parts. JFETs usually do better than bipolar in the ignoring-RFI department. The AD8220 is interesting, inexpensive, but for some reason distributors don't have any stock. Sold out? It does well for bandwidth at high gains, but not so well for CMRR at high frequency. The venerable INA110, for example, beats the pant off of it. -- Thanks, - Win
From: John Larkin on 20 Jun 2010 10:38 On 20 Jun 2010 05:38:13 -0700, Winfield Hill <Winfield_member(a)newsguy.com> wrote: >Paul Henderson wrote... >> >> I have previously used AMP 01, INA114 and AD620 instrumentation amps >> for EEG apps. All maximum gain 10,000. >> >> Since these packages are all about ten years old now, I would like to >> update my design, if appropriate. >> >> Can someone advise regarding more recent and better spec'd IC's of >> this general type? > > I recently finished updating our Selected Instrumentation Amps > table for H&H AoE III. Except for low-voltage-process designs, > I did not notice a lot of new activity in the last 15 years. > Most of the classic parts are doing fine, especially if they're > available in small SMT packages. > > Commenting on your choices, but for gains up to 1000 (most of > the data sheets don't address G=10k, that's a lot in one stage). > > The AMP01 comes in a large awkward package, but it seems to > do well at very high gains. However, it didn't make our list. > I wasn't able to find distributor inventory. Lack of interest? > > The INA114 is rather slow at high gains, the INA128 has similar > input characteristics, but is about 10x faster at high gains. > Both are fine at distributors, maybe the INA128 has the edge. > > The AD620 is a respectable part, popular, inexpensive. But > its 80dB CMRR at 10kHz pales compared to the INA128's 105dB. > The AD8221 is similar to the AD620, cheap, with 87dB CMRR. > The AD620 and AD8221 both let you directly bypass the input > transistors for RFI suppression. The INA128 may as well, but > TI hides the circuit details from the engineer. Too bad. > > You might want to consider some JFET parts. JFETs usually do > better than bipolar in the ignoring-RFI department. The AD8220 > is interesting, inexpensive, but for some reason distributors > don't have any stock. Sold out? It does well for bandwidth > at high gains, but not so well for CMRR at high frequency. > The venerable INA110, for example, beats the pant off of it. > On a current design, I had to make my own. I wanted lots of overvoltage protection, logic-switchable gains from 0.05 to 256, high precision, and at least +-12 volts of common-mode range, 120 dB CMRR at high gain. I wound up with a classic 3-opamp diffamp, using an LT1124 dual opamp, four Supertex depletion mode fets for protection, a discrete string of thinfilm resistors, one DPDT gain switch relay, two analog muxes, and an INA154 as the second stage. Two tiny trimpots tweak cmrr. Times 16 on one board. I'd love to get all that in a SO-8! John
From: Winfield Hill on 20 Jun 2010 11:29
John Larkin wrote... > > On a current design, I had to make my own. I wanted lots of > overvoltage protection, logic-switchable gains from 0.05 to 256, high > precision, and at least +-12 volts of common-mode range, 120 dB CMRR > at high gain. I wound up with a classic 3-opamp diffamp, using an > LT1124 dual opamp, four Supertex depletion mode fets for protection, a > discrete string of thinfilm resistors, one DPDT gain switch relay, two > analog muxes, and an INA154 as the second stage. Two tiny trimpots > tweak cmrr. Times 16 on one board. I'd love to get all that in a SO-8! Indeed. What was its CMRR at 1 and 10kHz, that's a tough region. -- Thanks, - Win |