使用頻率
REF6225、REF6230、REF633、，REF6250 SBOS748 3.1集成ADC驅(qū)動器緩沖器許多ADC數(shù)據(jù)表規(guī)定了REF引腳的平均電流消耗數(shù)微安。幾乎所有的電壓基準都提供這幾微安的平均電流；但并非所有電壓基準都適用于驅(qū)動高分辨率、高通量SAR ADC。電壓基準的最壞情況需求是在突發(fā)模式轉(zhuǎn)換期間，即ADC空閑很長時間后，轉(zhuǎn)換開始之前，并且預(yù)期轉(zhuǎn)換的第一個樣本是精確的。通常，在ADC的REF引腳和接地引腳之間（有時在REFP引腳和REFM引腳之間）連接一個大電容器，以平滑電流負載并減少電壓基準的負擔。電壓基準必須能夠提供對基準電容器完全充電所需的平均電流，但不會導(dǎo)致基準電壓顯著下降。大多數(shù)電壓基準缺乏對基準電容器完全充電的能力，并且當二進制加權(quán)電容器被切換到REF引腳時，由于輸出阻抗較大，電壓基準會穩(wěn)定下來。通常，電壓基準在高于100 Hz的頻率下具有10歐姆范圍內(nèi)的輸出阻抗。電壓基準的輸出電壓必須用低輸出阻抗（通常為高帶寬）放大器進行緩沖，以實現(xiàn)優(yōu)異的線性和失真性能。為高精度ADC設(shè)計參考緩沖器時要考慮的關(guān)鍵放大器規(guī)格是：低偏移、低漂移、寬帶寬和低輸出阻抗。雖然可以選擇一個充分滿足所有這些要求的放大器，但該放大器以過度功耗為代價。例如，OPA350是一款38 MHz帶寬放大器，最大偏置為0.5 mV，低偏置漂移為4μV/oC，但消耗的靜態(tài)電流為5.2mA。這是因為（從放大器設(shè)計的角度來看）偏移和漂移是直流規(guī)格，而帶寬、低輸出阻抗和高電容驅(qū)動能力是高頻規(guī)格。因此，在一個放大器中實現(xiàn)所有性
Frequency of use
REF6225, REF6230, REF633, REF6250 SBOS748 3.1 Integrated ADC Driver Buffer Many ADC data sheets specify the average current consumption of the REF pin in microamps. Almost all voltage references provide the average current of these microamps; However, not all voltage references are suitable for driving high-resolution, high-throughput SAR ADC. The worst case requirement of the voltage reference is that during the burst mode conversion, that is, after the ADC is idle for a long time, before the conversion starts, and the first sample of the expected conversion is accurate. Generally, a large capacitor is connected between the REF pin and the grounding pin of the ADC (sometimes between the REFP pin and the REFM pin) to smooth the current load and reduce the burden of the voltage reference. The voltage reference must be able to provide the average current required to fully charge the reference capacitor without causing a significant drop in the reference voltage. Most voltage references lack the ability to fully charge the reference capacitor, and when the binary weighted capacitor is switched to the REF pin, the voltage reference will stabilize due to the large output impedance. Typically, a voltage reference has an output impedance in the 10 ohm range at frequencies above 100 Hz. The output voltage of the voltage reference must be buffered with a low output impedance (usually high bandwidth) amplifier to achieve excellent linearity and distortion performance. The key amplifier specifications to consider when designing reference buffers for high-precision ADC are: low offset, low drift, broadband and low output impedance. Although it is possible to select an amplifier that fully meets all these requirements, this amplifier comes at the expense of excessive power consumption. For example, the OPA350 is a 38 MHz bandwidth amplifier with a maximum offset of 0.5 mV and a low offset drift of 4 μ V/o C, but consumes a quiescent current of 5.2 mA. This is because (from the perspective of amplifier design) offset and drift are DC specifications, while bandwidth, low output impedance and high capacitance drive capability are high-frequency specifications. Therefore, all performance is achieved in one amplifier
