Talk:DreamTeam/Brainduino: Difference between revisions
(gain calculation) |
(calculating expected gains) |
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Op amps ... | Op amps ... | ||
OPA2111 - what gain? expecting ~ 100 ? | OPA2111 - what gain? expecting ~ 100 ? | ||
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1 + (R23 + R24) / R27 ... | 1 + (R23 + R24) / R27 ... | ||
so 1 + (200 K / 2 K) = 101 | so 1 + (200 K / 2 K) = 101 | ||
so if input signal is on order of 100 microvolts | |||
then output of first amp will be 10.100 millivolts | |||
(really more like -50 to +50 microvolts -> -5 to +5 millivolts) | |||
AD8422 | |||
R5 and R6 are 200 ohms | |||
G = 1 + (19.8 kΩ/RG) | |||
= 1 + 99 = 100 | |||
??? also see fig. 56 on page 20 of http://www.analog.com/media/en/technical-documentation/data-sheets/AD8422.pdf | |||
now consider if input to AD8422 is on order of 10 millivolts | |||
output will be 1.000 volts | |||
(or if no offset voltage and input is actually ~ -5 to +5 millivolts, | |||
then output will be -0.5 to +0.5 volts) | |||
where might DC offset voltage come into play? | |||
2nd Stage AD8422 Instrumentation amp with gain resistor | 2nd Stage AD8422 Instrumentation amp with gain resistor |
Revision as of 23:36, 14 December 2016
what is value of c33? 50 pF or 1 nF ? determines high-cut frequency either 160 Hz (1 nF) or 3200 Hz (50 pF)
Op amps ...
OPA2111 - what gain? expecting ~ 100 ?
what values for R27, R23, R24 ? (also R28, R25, R26)
R27 should be 2K ohms R23, R24 -> 100K ohms
cf instrumentation amp (figure 9 of http://www.ti.com/lit/ds/symlink/opa2111.pdf) 1 + (R23 + R24) / R27 ... so 1 + (200 K / 2 K) = 101
so if input signal is on order of 100 microvolts then output of first amp will be 10.100 millivolts (really more like -50 to +50 microvolts -> -5 to +5 millivolts)
AD8422 R5 and R6 are 200 ohms G = 1 + (19.8 kΩ/RG) = 1 + 99 = 100
??? also see fig. 56 on page 20 of http://www.analog.com/media/en/technical-documentation/data-sheets/AD8422.pdf
now consider if input to AD8422 is on order of 10 millivolts output will be 1.000 volts (or if no offset voltage and input is actually ~ -5 to +5 millivolts, then output will be -0.5 to +0.5 volts)
where might DC offset voltage come into play?
2nd Stage AD8422 Instrumentation amp with gain resistor 2(10 kΩ + RREF)/(20 kΩ + RREF) http://www.analog.com/media/en/technical-documentation/data-sheets/AD8422.pdf In figure 56, you will see that an op amp is used to input to the VREF pin.
3rd stage Low-cut (aka high-pass ) filter and DC offset to 3rd Stage OP2177ARMZ ( IC1B Ch1 and IC1A Ch2 )
4th Stage IC3D>IC3C Ch1, and IC3A>IC3B, Potentially considered a two-pole high-cut(aka low-pass)