Electronic Components Datasheet Search |
|
LMK02000 Datasheet(PDF) 8 Page - Texas Instruments |
|
|
LMK02000 Datasheet(HTML) 8 Page - Texas Instruments |
8 / 14 page signalpath.national.com/designer SIGNAL PATH designer 7 the datasheet-specified, input common-mode-volt- age-range limits. For AC-coupled input operation, the input common mode will be at the same potential as the output common mode, or the VCM- pin voltage. For DC-coupled single-to-differential operation, the input common-mode voltage is the output common-mode voltage divided down by RF and RG. This is not an issue with split-voltage supplies such as ±5V. However, for single-supply operation such as GND and +10V, the divided- down-output common-mode voltage, appearing as the input common-mode voltage, must not exceed the amplifier’s rated operating-input common- mode-voltage range. Lack of headroom on the input can force the use of a negative rail lower than ground. For the best distortion performance, unlimited by amplifier input or output headroom, split ±5V supplies are recommended. An ideal amplifier for ADC driving would be completely transparent to the ADC and not degrade its performance. Although this is a challenge, it is possible to minimize performance degradation. From a DC-specification perspective, the most fundamental amplifier requirement is that the output-voltage range of the amplifier supports the ADC-input-voltage range for full-scale output. From an AC perspective, the amplifier must have flat bandwidth and gain such that the wanted signal is not attenuated by the amplifier’s frequency response, as well as low-enough noise and distortion levels that they do not impact the ADC’s performance. The required amplifier bandwidth is dictated by the input-signal-frequency spectrum to be processed and requirements for good distortion performance at high frequencies. The maximum signal frequency and the ADC’s full-scale input-voltage level determine the required amplifier slew rate and Large Signal Band- width (LSBW). These specifications determine the channel bandwidth when driving the ADC input at full scale. Due to the roll off of the amplifier open-loop gain, amplifier distortion starts to degrade at frequen- cies much lower than the amplifier LSBW. In the case of VFB amplifiers with a fixed-gain-bandwidth product, the amount of available gain for very-high- frequency signals can be limited. A CFB amplifier with relatively wide-gain independent bandwidth and excellent gain flatness is a good choice for very-high-frequency signals. The actual gain flat- ness required will depend on the application requirements. Assuming all of the other AC and DC specifications can be met, noise and distortion will ultimately be the two main specifications of interest for a given ADC and amplifier combination since these determine the SINAD. The ENOB can be calculated from the SINAD using the equation: ENOB = (SINAD - 1.76)/6.02, where SINAD is in dB Since distortion and noise are specified separately for the amplifier and ADC, it is necessary to look at how combining the amplifier with the ADC affects the overall subsystem’s performance. The noise of the driving amplifier and the noise of the ADC are uncorrelated and can be rss-summed together for the purpose of analysis. In order for the amplifier noise not to degrade the ADC performance, the amplifier output noise over the frequency band of interest ideally should be at least 6 dB less than the ADC input noise. The amplifier output-noise voltage spectral density measured in V/ Hz, is calculated by root-sum-squaring the output-noise voltage contributions arising from the amplifier’s input-voltage noise and current noise, with the additional noise of any external resistors around the amplifier. The total noise seen at the ADC input depends on the channel bandwidth, so it is critical to optimize the design for minimum acceptable band- width in order to maximize noise performance. Unless limited by a channel filter, noise and distortion prod- ucts from the entire amplifier bandwidth will all be sampled by the ADC and aliased back down into the 1st Nyquist zone. In addition to band-limiting to fS/2, the channel filter is chosen to limit the amplifier-noise bandwidth and attenuate any distortion products. Ideally, any in-band, amplifier-distortion products should be 6 dB lower than the ADC’s own distortion products. Choosing the sample frequency carefully SignalPathDesigner.indd 7 SignalPathDesigner.indd 7 9/5/07 3:24:35 PM 9/5/07 3:24:35 PM |
Similar Part No. - LMK02000 |
|
Similar Description - LMK02000 |
|
|
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 |