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Calculating maximum power delivered to load for current steering DACs

Calculating maximum power delivered to load for current steering DACs. Calculations. Calculate the peak-to-peak voltage at the output of the DAC Vdac p -p = I FS * R Where R is the total impedance seen by the DAC and I FS is the full-scale output current

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Calculating maximum power delivered to load for current steering DACs

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  1. Calculating maximum power delivered to load for current steering DACs

  2. Calculations • Calculate the peak-to-peak voltage at the output of the DAC • Vdacp-p= IFS * R • Where R is the total impedance seen by the DAC and IFS is the full-scale output current • Find voltage at load by dividing by the sqrt of the impedance ratio • Vloadp-p= Vdacp-p/ sqrt(NImp) • Where sqrt(Nimp) = 2 for 4:1 trans, 1.414 for 2:1 trans, 1 for 1:1 trans • Convert peak-to-peak voltage to rms voltage • Vloadrms= Vloadp-p/ (2 * sqrt(2) ) • Calculate power DELIVERED to the load • Pload= (Vloadrms)2 / RL • RL is the impedance after the transformer, probably 50 ohms such as in the case of a spectrum analyzer hooked up to the transformer output • Convert power to dBm • PdBm = 10 * log(Pload / 1 mW)

  3. Example 1:1 transformer Vdacp-p= (20 mA) * ((50+50) // 100 // 50) = 500 mV (25 ohm total load) Vloadp-p= 500 mV / sqrt(1) = 500 mV Vloadrms= 500 mV / (2 * sqrt(2) ) = 176.8 mV Pload= (176.8 mV)2/ 50 = 625.2 uW (spectrum analyzer = 50 ohm load) PdBm = 10 * log(625.2 uW / 1 mW) = -2.04 dBm

  4. Example 2:1 transformer Vdacp-p= (20 mA) * ((50+50) // (2*50)) = 1 V (50 ohm total load) Vloadp-p= 1 V / sqrt(2) = 707.2 mV Vloadrms = 707.2 mV / (2 * sqrt(2) ) = 250 mV Pload= (250 mV)2/ 50 = 1.25 mW (spectrum analyzer = 50 ohm load) PdBm = 10 * log(1.25 mW / 1 mW) = 0.969 dBm

  5. Example 4:1 transformer Vdacp-p = (20 mA) * ((100+100) // (4*50)) = 2 V (100 ohm total load) Vloadp-p = 2 V / sqrt(4) = 1 V Vloadrms = 1 V / (2 * sqrt(2) ) = 353.6 mV Pload = (353.6 mV)2 / 50 = 2.5 mW (spectrum analyzer = 50 ohm load) PdBm = 10 * log(2.5 mW / 1 mW) = 3.98 dBm

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