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CLC446 Datasheet(PDF) 7 Page - National Semiconductor (TI) |
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CLC446 Datasheet(HTML) 7 Page - National Semiconductor (TI) |
7 / 12 page 7 http://www.national.com Using a resistor in series with a reactive load will also reduce the load’s effect on amplifier loop dynamics. For instance, driving coaxial cables without an output series resistor may cause peaking or oscillation. Transmission Line Matching One method for matching the characteristic impedance of a transmission line is to place the appropriate resistor at the input or output of the amplifier. Figure 7 shows the typical circuit configurations for matching transmission lines. Figure 7: Transmission Line Matching In non-inverting gain applications, Rg is connected directly to ground. The resistors R1, R2, R6, and R7 are equal to the characteristic impedance, Zo, of the transmission line or cable. Use R3 to isolate the amplifier from reactive loading caused by the transmis- sion line, or by parasitics. In inverting gain applications, R3 is connected directly to ground. The resistors R4, R6, and R7 are equal to Zo. The parallel combination of R5 and Rg is also equal to Zo. The input and output matching resistors attenuate the signal by a factor of 2, therefore additional gain is needed. Use C6 to match the output transmission line over a greater frequency range. It compensates for the increase of the op amp’s output impedance with frequency. Thermal Design To calculate the power dissipation for the CLC446, follow these steps: 1. Calculate the no-load op amp power: Pamp = ICC • (VCC – VEE) 2. Calculate the output stage’s RMS power: Po = (VCC – Vload) • Iload, where Vload and Iload are the RMS voltage and current across the external load. 3. Calculate the total op amp RMS power: Pt = Pamp + Po To calculate the maximum allowable ambient tempera- ture, solve the following equation: Tamb = 175 – Pt • θJA, where θ JA is the thermal resistance from junction to ambient in °C/W, and Tamb is in °C. The Package Thermal Resistance section contains the thermal resistance for various packages. Dynamic Range (input /output protection) ESD diodes are present on all connected pins for protection from static voltage damage. For a signal that may exceed the supply voltages, we recommend using diode clamps at the amplifier’s input to limit the signals to less than the supply voltages. Dynamic Range (input /output levels) The Electrical Characteristics section specifies the Common-Mode Input Range and Output Voltage Range; these voltage ranges scale with the supplies. Output Current is also specified in the Electrical Characteristics section. Unity gain applications are limited by the Common-Mode Input Range. At greater non-inverting gains, the Output Voltage Range becomes the limiting factor. Inverting gain applications are limited by the Output Voltage Range. For transimpedance gain applications, the sum of the input currents injected at the inverting input pin of the op amp needs to be: , where Vmax is the Output Voltage Range (see the DC Gain (transimpedance) sub-section for details). The equivalent output load needs to be large enough so that the minimum output current can produce the required output voltage swing. See the DC Design (out- put loading) sub-section for details. Dynamic Range (noise) In RF applications, noise is frequently specified as Noise Figure (NF). This allows the calculation of signal to noise ratio into a defined load. Figure 8 plots the NF for a CLC446 at a gain of 10, and with a feedback resistor Rf of 100 Ω. The minimum NF (3.9dB) occurs when the source impedance equals 1600 Ω. Figure 8: Noise Figure vs. Source Resistance Figure 9: Noise Model + - CLC446 R3 Z0 R6 Vo Z0 R1 R2 + - Rg Z0 R4 R5 V1 V2 +- Rf C6 R7 I V R in max f ≤ Source Resistance ( Ω) 20 15 0 10 100 10k 10 5 1k 100k + - CLC446 eni2 Vo Rs ibn2 + - Vs Rf ibi2 Rg |
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Similar Description - CLC446 |
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