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ADA4805-2ACPZ-R7 数据表(PDF) 19 Page - Analog Devices |
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ADA4805-2ACPZ-R7 数据表(HTML) 19 Page - Analog Devices |
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19 / 25 page ![]() Data Sheet ADA4805-1/ADA4805-2 NOISE CONSIDERATIONS Figure 54 illustrates the primary noise contributors for the typical gain configurations. The total output noise (vn_out) is the root sum square of all the noise contributions. RG RS in– RF vn 4kTRS vn_RS = 4kTRG vn_RG = vn_RF = + vn_out – 4kTRF in+ Figure 54. Noise Sources in Typical Connection The output noise spectral density is calculated by [ ] 2 2 2 2 2 2 2 _ 4 4 1 4 F n G G F n S n G F F out n R i kTR R R v R i kTRs R R kTR v − + + + + + + + = where: k is Boltzmann’s constant. T is the absolute temperature in degrees Kelvin. RF and RG are the feedback network resistances, as shown in Figure 54. RS is the source resistance, as shown in Figure 54. in+ and in− represent the amplifier input current noise spectral density in pA/√Hz. vn is the amplifier input voltage noise spectral density in nV/√Hz. Source resistance noise, amplifier input voltage noise (vn), and the voltage noise from the amplifier input current noise (in+ × RS) are all subject to the noise gain term (1 + RF/RG). Figure 55 shows the total referred to input (RTI) noise due to the amplifier vs. the source resistance. Note that with a 5.9 nV/√Hz input voltage noise and 0.6 pA/√Hz input current noise, the noise contributions of the amplifier are relatively small for source resistances from approximately 2.6 kΩ to 47 kΩ. The Analog Devices silicon germanium (SiGe) bipolar process makes it possible to achieve a low noise of 5.9 nV/√Hz for the ADA4805-1/ADA4805-2. This noise is much improved compared to similar low power amplifiers with a supply current in the range of hundreds of microamperes. 1 10 100 1000 100 1k 10k 100k 1M SOURCE RESIST ANCE (Ω) TOTAL NOISE SOURCE RESISTANCE NOISE AMPLIFIER NOISE SOURCE RESIST ANCE = 2.6kΩ SOURCE RESIST ANCE = 47kΩ Figure 55. RTI Noise vs. Source Resistance Rev. B | Page 19 of 25 |
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