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A peak current and noise absorbing design

In Electronic Infomation Category: A | on April 18,2011

When you are in the system using a 8-14 Analog to Digital Converter (ADC), the understanding of the converter voltage reference channel is crucial. Figure 1 shows the ADC reference input can be adapted to a dynamic circuit. Figure, the voltage reference chip capacitors CL1 for the conversion process and CL253 datasheet and provides the base voltage (voltage-foundation), designed to absorb the internal ADC reference circuit [REF 1] peak current and CL253 price and filter reference noise. The circuit, not only reduce the voltage reference noise is important, the stability of the internal voltage reference amplifier is also important to balance.


Figure 1 in the reference and CL253 suppliers and the ADC is installed between the low-pass filter 8-14 ADC voltage reference circuit in series

Use of the circuit to solve the noise problem, ADC transfer function (equation 1) show that the voltage reference noise.

(equation 1)

Formula, VIN for the ADCs input voltage, N is the median ADC, while the reference voltage VREF for the ADC. VREF variable includes all errors associated with the reference chip, such as: accuracy, temperature changes and noise. Any case, the reference error will become part of ADC system gain error.

You can use the system processor or controller, the majority of these errors in the calibration. If you are from the ADC negative full scale to positive full-scale measurements on several points, you will see these errors in the gain error, the input of the converter voltage. You can not use the processor or controller calibration error is noise. Figure 2, you will see a reference to the output converter with analog input voltage noise is increasing.


Figure 2 ADC noise voltage reference and the converter output code of

Most of the voltage reference data table has a frequency range of 0.1 to 10Hz Output voltage noise specifications. Some manufacturers provide a voltage reference output noise density specifications. Such norms are generally used for regional broadband noise, for example: 10kHz noise density. No matter how the provisions of the reference noise makers, adding reference low-pass filter can reduce the overall noise output. You can use a capacitor and capacitor equivalent series resistance (ESR) to design this filter (see Figure 1). You can also reference 2 by using the same techniques recommended method to ensure the stability of the design.

Figure 1 shows the configuration we assume in the 8-14 converter complete circuit reference system. The systems voltage reference accuracy is important; however, you can use any hardware or software error on the initial calibration. On the other hand, the absorption peak ADC reference pin on the current reference, while eliminating or reducing noise, requires a degree of characterization and hardware filtering techniques.

Next time, we will study and design of a 16-bit and above for the converter voltage reference circuit.

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