 |
 |
|
 |
 |
||
|
Volume 9, Issue 2 | YOUR SEMICONDUCTOR SOLUTIONS RESOURCE |
|
||
|
C o n t e n t s 16-Bit ADCs Deliver Ease of Use >> Benefits of Continuous Time Σ-Δ ADCs >> 24-Bit Σ-Δ ADC for Faster Precision Measurement >> High Speed ADCs Use 50% Less PCB Surface >> Receivers Optimize Image Quality and Power >> Pin-Programmable, Low Power Σ-Δ ADC Is Easy to Implement >> ADC Simulation, Software, and Behavioral Tools >> New Family of PulSAR ADCs Delivers High Resolution >> Dual Channel, SAR ADCs with Highest Performance at Lowest Power >> Top Considerations for Avoiding Differential ADC Driver Accidents >> ADC Drivers Designed to Get Peak Performance Out of Your ADC >> VGAs for Driving High Speed ADCs >> Fully Differential IF Amplifiers >> Current Feedback Differential ADC Drivers for High Gain >> 16-Bit ADC Driver Simplifies Signal Conditioning >> ADC Driver Supports Converter Performance >> All prices in this bulletin are in USD in quantities greater than 1000 (unless otherwise noted), recommended lowest grade resale, FOB U.S.A.
|
|
|
|
Top Considerations for Avoiding Differential ADC Driver Accidents
Noise and distortion are two important parameters to consider when selecting an ADC driver because they directly impact overall ADC performance. Both affect the ADC's effective number of bits (ENOB). There are also many other parameters and configurations to consider when selecting an ADC driver; listed below is a short list of critical and subtle issues to be aware of when reviewing driver specifications. Noise Noise is everywhere, and minimizing the amount of noise added by a driver is critical. Driver noise contribution yielding less than 0.5 LSB (least significant bit) error is usually acceptable. Review the noise for each driver against other specifications, such as supply current, as there is typically a performance trade-off. Distortion Ideally, the harmonic distortion (HD) performance of the driver should be better than that of the ADC. When this performance is not possible, the driver must be evaluated by analyzing the HD performance level at the frequency of concern. As in the noise example noted above, the HD contribution to the ENOB must be calculated and evaluated to achieve the required system performance. Input Common-Mode Voltage Range (ICMVR) ICMVR is a common area of confusion and a common cause for mistakes. Most often the source of trouble stems from applying a bipolar input to a driver operating from a single supply. Some drivers can tolerate this configuration well, but others cannot. For best results, make sure the driver is compatible with your application by checking the ICMVR specifications in the driver data sheet. Input Drive—Single-Ended, Differential, and Termination Is the input driven single-ended or differentially? Does it require a termination or is it being driven from a low impedance source? If it does require termination, what is the proper method? AC-Coupled/DC-Coupled Does the driver need to be ac-coupled/dc-coupled? This requirement has many implications in terms of the signal path construction. The VOCM pin of the driver can be especially important here. An ac-coupled system may be required because of voltage incompatibilities or other system requirements where the input signal level is not compatible with that of the driver or ADC. In these cases, the input signal level needs to be rebiased. The limitation on ac coupling is that the input cannot go all the way down to dc. The ability to shift the output using the VOCM pin in these applications is especially helpful. Much the same can be said for dc-coupled applications; the benefit of dc-coupled applications is fewer components and lower frequency operation.Output Swing ADCs perform best when their entire input range is utilized. Therefore, matching the output swing of the driver to the ADC input is critical. Some drivers can swing rail-to-rail; others have a headroom restriction that limits the output swing. This restriction is not necessarily a disadvantage as it can provide built-in swing limitation and prevent overdriving the ADC input. Supply Voltage A quick way to narrow down your ADC driver choices is the power supply requirement. System requirements will dictate which drivers can be used based on the operating voltages available. The supply voltage of the driver affects numerous parameters ranging from bandwidth to output swing. Driver performance can vary from driver to driver, even with the same power supply; therefore, it is critical to review the driver data sheet to ensure the required performance vs. power supply is attainable. Bandwidth and Slew Rate The bandwidth and slew rate of a driver describe how accurately it can faithfully reproduce a high speed signal. Differential drivers must be able to replicate high speed signals to maintain proper signal fidelity throughout the signal path. To minimize amplitude errors, a good rule of thumb is that the driver should have 5× the bandwidth of the signal being sampled to keep amplitude errors under 1%.
|
|
