数据搜索系统,热门电子元器件搜索 |
|
LM1972N 数据表(PDF) 8 Page - National Semiconductor (TI) |
|
|
LM1972N 数据表(HTML) 8 Page - National Semiconductor (TI) |
8 / 11 page Application Information (Continued) DAISY-CHAIN CAPABILITY Since the µPot’s digital interface is essentially a shift register, multiple µPots can be programmed utilizing the same data and load/shift lines. As shown in Figure 11, for an n-µPot daisy-chain, there are 16n bits to be shifted and loaded for the chain. The data loading sequence is the same for n-µPots as it is for one µPot. First the LOAD/SHIFT line goes low, then the data is clocked in sequentially while the preced- ing data in each µPot is shifted out the DATA-OUT pin to the next µPot in the chain or to ground if it is the last µPot in the chain. Then the LOAD/SHIFT line goes high; latching the data into each of their corresponding µPots. The data is then decoded according to the address (channel selection) and the appropriate tap switch controlling the attenuation level is selected. CROSSTALK MEASUREMENTS The crosstalk of a µPot as shown in the Typical Perfor- mance Characteristics section was obtained by placing a signal on one channel and measuring the level at the output of another channel of the same frequency. It is important to be sure that the signal level being measured is of the same frequency such that a true indication of crosstalk may be ob- tained. Also, to ensure an accurate measurement, the mea- sured channel’s input should be AC grounded througha1µF capacitor. CLICKS AND POPS So, why is that output buffer needed anyway? There are three answers to this question, all of which are important from a system point of view. The first reason to utilize a buffer/amplifier at the output of a µPot is to ensure that there are no audible clicks or pops due to attenuation step changes in the device. If an on-board bi- polar op amp had been used for the output stage, its require- ment of a finite amount of DC bias current for operation would cause a DC voltage “pop” when the output impedance of the µPot changes. Again, this phenomenon is due to the fact that the output impedance of the µPot is changing with step changes and a bipolar amplifier requires a finite amount of DC bias current for its operation. As the impedance changes, so does the DC bias current and thus there is a DC voltage “pop”. Secondly, the µPot has no drive capability, so any desired gain needs to be accomplished through a buffer/ non-inverting amplifer. Third, the output of a µPot needs to see a high impedance to prevent loading and subsequent linearity errors from ocur- ring. A JFET input buffer provides a high input impedance to the output of the µPot so that this does not occur. Clicks and pops can be avoided by using a JFET input buffer/amplifier such as an LF412ACN. The LF412 has a high input impedance and exhibits both a low noise floor and low THD+N throughout the audio spectrum which maintains signal integrity and linearity for the system. The performance of the system solution is entirely dependent upon the quality and performance of the JFET input buffer/amplifier. LOGARITHMIC GAIN AMPUFIER The µPot is capable of being used in the feedback loop of an amplifier, however, as stated previously, the output of the µPot needs to see a high impedance in order to maintain its high performance and linearity. Again, loading the output will change the values of attenuation for the device. As shown in Figure 10, a µPot used in the feedback loop creates a loga- rithmic gain amplifier. In this configuration the attenuation levels from Table 1, now become gain levels with the largest possible gain value being 78dB. For most applications 78dB of gain will cause signal clipping to occur, however, because of the µPot’s versatility the gain can be controlled through programming such that the clipping level of the system is never obtained. An important point to remember is that when in mute mode the input is disconnected from the output. In this configuration this will place the amplifier in its open loop gain state, thus resulting in severe comparator action. Care should be taken with the programming and design of this type of circuit. To provide the best performance, a JFET input amplifier should be used. DS011978-11 FIGURE 9. µPot System Architecture www.national.com 8 |
类似零件编号 - LM1972N |
|
类似说明 - LM1972N |
|
|
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 |