数据搜索系统,热门电子元器件搜索 |
|
AD621AR 数据表(PDF) 10 Page - Analog Devices |
|
AD621AR 数据表(HTML) 10 Page - Analog Devices |
10 / 16 page AD621 REV. B –10– +VS –VS I1 20 A A1 C1 C2 R1 25k R5 5555.6 Q1 G = 100 R6 555.6 R3 400 –IN 2 4 1 R4 400 3 +IN 10k 10k OUTPUT 5 6 A3 – – + I2 20 A VB A2 R2 25k 10k 10k Q2 G = 100 8 REF 7 Figure 3. Simplified Schematic of AD621 THEORY OF OPERATION The AD621 is a monolithic instrumentation amplifier based on a modification of the classic three op amp circuit. Careful layout of the chip, with particular attention to thermal symmetry builds in tight matching and tracking of critical components, thus preserving the high level of performance inherent in this circuit, at a low price. On chip gain resistors are pretrimmed for gains of 10 and 100. The AD621 is preset to a gain of 10. A single external jumper (between Pins 1 and 8) is all that is needed to select a gain of 100. Special design techniques assure a low gain TC of 5 ppm/ °C max, even at a gain of 100. Figure 3 is a simplified schematic of the AD621. The input transistors Q1 and Q2 provide a single differential-pair bipolar input for high precision, yet offer 10 × lower Input Bias Current, thanks to Super βeta processing. Feedback through the Q1-A1-R1 loop and the Q2-A2-R2 loop maintains constant collector cur- rent of the input devices Q1 and Q2, thereby impressing the input voltage across the gain-setting resistor, RG, which equals R5 at a gain of 10 or the parallel combination of R5 and R6 at a gain of 100. This creates a differential gain from the inputs to the A1/A2 outputs given by G = (R1 + R2) / RG + 1. The unity-gain subtracter A3 removes any common-mode signal, yielding a single-ended output referred to the REF pin potential. The value of RG also determines the transconductance of the preamp stage. As RG is reduced for larger gains, the transcon- ductance increases asymptotically to that of the input transistors. This has three important advantages: (a) Open-loop gain is boosted for increasing programmed gain, thus reducing gain- related errors. (b) The gain-bandwidth product (determined by C1, C2 and the preamp transconductance) increases with pro- grammed gain, thus optimizing frequency response. (c) The input voltage noise is reduced to a value of 9 nV/ √Hz, deter- mined mainly by the collector current and base resistance of the input devices. Make vs. Buy: A Typical Bridge Application Error Budget The AD621 offers improved performance over discrete three op amp IA designs, along with smaller size, fewer components and 10 times lower supply current. In the typical application, shown in Figure 4, a gain of 100 is required to amplify a bridge output of 20 mV full scale over the industrial temperature range of –40 °C to +85 °C. The error budget table below shows how to calculate the effect various error sources have on circuit accuracy. Regardless of the system it is being used in, the AD621 provides greater accuracy, and at low power and price. In simple systems, absolute accuracy and drift errors are by far the most significant contributors to error. In more complex systems with an intelligent processor, an autogain/autozero cycle will remove all absolute accuracy and drift errors leaving only the resolution errors of gain nonlinearity and noise, thus allowing full 14-bit accuracy. Note that for the discrete circuit, the OP07 specifications for input voltage offset and noise have been multiplied by 2. This is because a three op amp type in amp has two op amps at its inputs, both contributing to the overall input error. OP07D OP07D – + 10k * 10k * 10k * 10k * OP07D – + 10k ** 10k ** + – 3 OP AMP, IN AMP, G = 100 * 0.02% RESISTOR MATCH, 3PPM/ C TRACKING ** DISCRETE 1% RESISTOR, 100PPM/ C TRACKING SUPPLY CURRENT = 15mA MAX + – AD621A REFERENCE AD621A MONOLITHIC INSTRUMENTATION AMPLIFIER, G = 100 SUPPLY CURRENT = 1.3mA MAX 10V R = 350 R = 350 R = 350 R = 350 PRECISION BRIDGE TRANSDUCER 100k ** Figure 4. Make vs. Buy |
类似零件编号 - AD621AR |
|
类似说明 - AD621AR |
|
|
链接网址 |
隐私政策 |
ALLDATASHEETCN.COM |
ALLDATASHEET是否为您带来帮助? [ DONATE ] |
关于 Alldatasheet | 广告服务 | 联系我们 | 隐私政策 | 链接交换 | 制造商名单 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 |