 |
数据搜索系统，热门电子元器件搜索 |
|
|
数据搜索系统，热门电子元器件搜索 |
|
ADA4927-2YCPZ-R2 数据表(PDF) 19 Page - Analog Devices |
|
|
|||||||||||||||||||||||||||||
ADA4927-2YCPZ-R2 数据表(HTML) 19 Page - Analog Devices |
|
|
19 / 24 page  ADA4927-1/ADA4927-2 Rev. 0 | Page 19 of 24 For an unbalanced, single-ended input signal (see Figure 49), the input impedance is () ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ + × − = F G F G SE IN R R R R R 2 1 , ADA4927 RL VOUT, dm +VS –VS RG RG RF RF VOCM RIN, SE Figure 49. The ADA4927 with Unbalanced (Single-Ended) Input The input impedance of the circuit is effectively higher than it would be for a conventional op amp connected as an inverter because a fraction of the differential output voltage appears at the inputs as a common-mode signal, partially bootstrapping the voltage across the input resistor RG. The common-mode voltage at the amplifier input terminals can be easily determined by noting that the voltage at the inverting input is equal to the noninverting output voltage divided down by the voltage divider formed by RF and RG in the lower loop. This voltage is present at both input terminals due to negative voltage feedback and is in phase with the input signal, thus reducing the effective voltage across RG in the upper loop and partially bootstrapping RG. Terminating a Single-Ended Input This section deals with how to properly terminate a single- ended input to the ADA4927 with a gain of 1, RF = 348 Ω, and RG = 348 Ω. An example using an input source with a terminated output voltage of 1 V p-p and a source resistance of 50 Ω illustrates the four simple steps that must be followed. Note that, because the terminated output voltage of the source is 1 V p-p, the open circuit output voltage of the source is 2 V p-p. The source shown in Figure 50 indicates this open-circuit voltage. 1. The input impedance must be calculated using the following formula: Ω 464 ) 348 348 ( 2 348 1 348 ) ( 2 1 = ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ + × − = ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ + × − = F G F G IN R R R R R RS 50Ω VS 2V p-p RIN 464Ω ADA4927 RL VOUT, dm +VS –VS RG 348Ω RG 348Ω RF 348Ω RF 348Ω VOCM Figure 50. Calculating Single-Ended Input Impedance RIN 2. To match the 50 Ω source resistance, the termination resistor, RT, is calculated using RT||464 Ω = 50 Ω. The closest standard 1% value for RT is 56.2 Ω. ADA4927 RL VOUT, dm +VS –VS RS 50Ω RG 348Ω RG 348Ω RF 348Ω RF 348Ω VOCM VS 2V p-p RIN 50Ω RT 56.2Ω Figure 51. Adding Termination Resistor RT 3. It can be seen from Figure 51 that the effective RG in the upper feedback loop is now greater than the RG in the lower loop due to the addition of the termination resistors. To compensate for the imbalance of the gain resistors, a correction resistor (RTS) is added in series with RG in the lower loop. RTS is equal to the Thevenin equivalent of the source resistance RS and the termination resistance RT and is equal to RS||RT. RS 50Ω VS 2V p-p RT 56.2Ω RTH 26.5Ω VTH 1.06V p-p Figure 52. Calculating the Thevenin Equivalent |
|
|
链接网址 |
| 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 | 数据表链接 | 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 |
Chinese ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
