ADC Drivers & Filters: Single Ended Buffer

Figure 1 shows a recommended single ended buffered drive circuit using the LT1818 in unity gain mode. The 47pF capacitor from AIN to ground and 50Ω source resistor limits the input bandwidth to 68MHz. The 47pF capacitor also acts as a charge reservoir for the input sample-and-hold and isolates the LT1818 from sampling glitch kick-back. The 50Ω source resistor is used to help stabilize the settling response of the drive amplifier. When choosing values of source resistance and shunt capacitance, the drive amplifier data sheet should be consulted and followed for optimum settling response. If lower input bandwidths are desired, care should be taken to optimize the settling response of the driver amplifier with higher values of shunt capacitance or series resistance. High quality capacitors and resistors should be used in the RC filter since these components can add distortion. NP0/C0G and silver mica type dielectric capacitors have excellent linearity. Carbon surface mount resistors can generate distortion from self heating and from damage that may occur during soldering. Metal film surface mount resistors are much less susceptible to both problems. When high amplitude unwanted signals are close in frequency to the desired signal frequency, a multiple pole filter is required. High external source resistance, combined with external shunt capacitance at Pin 4 and 13pF of input capacitance on the LTC2314-14 in sample mode, will significantly reduce the internal 130MHz input bandwidth and may increase the required acquisition time beyond the minimum acquisition time (tACQ-MIN) of 40ns.

Figure 1. RC Input Filter



Guy Hoover

Guy Hoover是一名拥有超过30年凌力尔特公司工作经验的工程师,曾担任技术员、IC设计工程师和应用工程师。

T他的职业生涯始于LTC,当时的职位是技术员,并向参与多个产品工作的Bob Dobkin、Bob Widlar、Carl Nelson和Tom Redfern学习,涉及产品包括运算放大器、比较器、开关稳压器和ADC。在此期间,他还花了大量时间来编写测试程序以对这些器件的特性进行表征。

他在LTC的下一段职业生涯是学习PSpice和设计SAR ADC。由Guy设计的产品包括LTC1197系列10位ADC和LTC1864系列12位和16位ADC。

Guy目前是混合信号部的应用工程师,专门从事SAR ADC应用支持工作。这包括为SAR ADC演示板设计、编写Verilog代码和测试程序,帮助客户优化包含LTC SAR ADC的产品,并希望编写有用的应用文章,将有关使用这些器件的知识传递给客户。