Electronic Components Datasheet Search |
|
AD624ACHIPS Datasheet(PDF) 7 Page - Analog Devices |
|
AD624ACHIPS Datasheet(HTML) 7 Page - Analog Devices |
7 / 15 page REV. C AD624 –7– AD624 +VS VOUT 10k 1% 1k 10T 10k 1% RG1 G = 100 G = 200 G = 500 RG2 –VS 200 0.1% 100k 1% 500 0.1% 1k 0.1% INPUT 20V p-p Figure 25. Settling Time Test Circuit THEORY OF OPERATION The AD624 is a monolithic instrumentation amplifier based on a modification of the classic three-op-amp instrumentation amplifier. Monolithic construction and laser-wafer-trimming allow the tight matching and tracking of circuit components and the high level of performance that this circuit architecture is ca- pable of. A preamp section (Q1–Q4) develops the programmed gain by the use of feedback concepts. Feedback from the outputs of A1 and A2 forces the collector currents of Q1–Q4 to be constant thereby impressing the input voltage across RG. The gain is set by choosing the value of RG from the equation, Gain = 40 k RG + 1. The value of RG also sets the transconduct- ance of the input preamp stage increasing it asymptotically to the transconductance of the input transistors as RG is reduced for larger gains. This has three important advantages. First, this approach allows the circuit to achieve a very high open loop gain of 3 × 108 at a programmed gain of 1000 thus reducing gain related errors to a negligible 3 ppm. Second, the gain bandwidth product which is determined by C3 or C4 and the input trans- conductance, reaches 25 MHz. Third, the input voltage noise reduces to a value determined by the collector current of the input transistors for an RTI noise of 4 nV/ √Hz at G ≥ 500. AD624 +VS 100 200 RG2 –VS 16.2k +VS 1/2 AD712 9.09k G1, 100, 200 1k 1 F G500 100 1 F 1.62M –VS 1 F 16.2k 1.82k 500 1/2 AD712 Figure 26. Noise Test Circuit INPUT CONSIDERATIONS Under input overload conditions the user will see RG + 100 Ω and two diode drops (~1.2 V) between the plus and minus inputs, in either direction. If safe overload current under all conditions is assumed to be 10 mA, the maximum overload voltage is ~ ±2.5 V. While the AD624 can withstand this con- tinuously, momentary overloads of ±10 V will not harm the device. On the other hand the inputs should never exceed the supply voltage. The AD524 should be considered in applications that require protection from severe input overload. If this is not possible, external protection resistors can be put in series with the inputs of the AD624 to augment the internal (50 Ω) protection resis- tors. This will most seriously degrade the noise performance. For this reason the value of these resistors should be chosen to be as low as possible and still provide 10 mA of current limiting under maximum continuous overload conditions. In selecting the value of these resistors, the internal gain setting resistor and the 1.2 volt drop need to be considered. For example, to pro- tect the device from a continuous differential overload of 20 V at a gain of 100, 1.9 k Ω of resistance is required. The internal gain resistor is 404 Ω; the internal protect resistor is 100 Ω. There is a 1.2 V drop across D1 or D2 and the base-emitter junction of either Q1 and Q3 or Q2 and Q4 as shown in Figure 27, 1400 Ω of external resistance would be required (700 Ω in series with each input). The RTI noise in this case would be 4 KTRext +(4 nV / Hz )2 = 6.2 nV / Hz 50 13 50 A I1 50 A C3 I2 50 A R57 20k R56 20k 500 SENSE +IN VO REF I4 50 A 200 100 4445 80.2 124 225.3 –IN –VS RG1 RG2 C4 VB A2 R52 10k R55 10k A3 R53 10k R54 10k +VS 50 Q1, Q3 Q2, Q4 A1 Figure 27. Simplified Circuit of Amplifier; Gain Is Defined as (R56 + R57)/(RG) + 1. For a Gain of 1, RG Is an Open Circuit. INPUT OFFSET AND OUTPUT OFFSET Voltage offset specifications are often considered a figure of merit for instrumentation amplifiers. While initial offset may be adjusted to zero, shifts in offset voltage due to temperature variations will cause errors. Intelligent systems can often correct for this factor with an autozero cycle, but there are many small- signal high-gain applications that don’t have this capability. Voltage offset and offset drift each have two components; input and output. Input offset is that component of offset that is |
Similar Part No. - AD624ACHIPS |
|
Similar Description - AD624ACHIPS |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |