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CA3060 データシート(PDF) 7 Page - Harris Corporation |
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CA3060 データシート(HTML) 7 Page - Harris Corporation |
7 / 12 page 3-7 Application Information The CA3060 consists of three operational amplifiers similar in form and application to conventional operational amplifiers but sufficiently different from the standard operational amplifier (op amp) to justify some explanation of their characteristics. The amplifiers incorporated in the CA3060 are best described by the term Operational Transconduc- tance Amplifier (OTA). The characteristics of an ideal OTA are similar to those of an ideal op amp except that the OTA has an extremely high output impedance. Because of this inherent characteristics the output signal is best defined in terms of current which is proportional to the difference between the voltages of the two input terminals. Thus, the transfer characteristics is best described in terms of transconductance rather than voltage gain. Other than the difference given above, the characteristics tabulated are similar to those of any typical op amp. The OTA circuitry incorporated in the CA3060 (Figure 18) provides the equipment designer with a wider variety of circuit arrangements than does the standard op amp; because as the curves indicate, the user may select the optimum circuit conditions for a specific application simply by varying the bias conditions of each amplifier. If low power consumption, low bias, and low offset current, or high input impedance are primary design requirements, then low current operating conditions may be selected. On the other hand, if operation into a moderate load impedance is the primary consideration, then higher levels of bias may be used. Bias Consideration for Op Amp Applications The operational transconductance amplifiers allow the circuit designer to select and control the operating conditions of the circuit merely by the adjustment of the amplifier bias current IABC. This enables the designer to have complete control over transconductance, peak output current and total power consumption independent of supply voltage. In addition, the high output impedance makes these amplifi- ers ideal for applications where current summing is involved. The design of a typical operational amplifier circuit (Figure 19) would proceed as follows: Circuit Requirements Closed Loop Voltage Gain = 10 (20dB) Offset Voltage Adjustable to Zero Current Drain as Low as Possible Supply Voltage = ±6V Maximum Input Voltage = ±50mV Input Resistance = 20k Ω Load Resistance = 20k Ω Device: CA3060 Calculation 1. Required Transconductance g21. Assume that the open loop gain AOL must be at least ten times the closed loop gain. Therefore, the forward transconductance required is given by: g21 = AOL/RL = 100/18k Ω ≅ 5.5mS (RL = 20kΩ in parallel with 200kΩ≅ 18kΩ) 2. Selection of Suitable Amplifier Bias Current. The ampli- fier bias current is selected from the minimum value curve of transconductance (Figure 11) to assure that the amplifi- er will provide sufficient gain. For the required g21 of 5.5mS an amplifier bias current IABC of 20µA is suitable. 3. Determination of Output Swing Capability. For a closed loop gain of 10 the output swing is ±0.5V and the peak load current is 25 µA. However, the amplifier must also supply the necessary current through the feedback resistor and if RS = 20kΩ, then RF = 200kΩ for ACL = 10. Therefore, the feedback loading = 0.5V/200k Ω = 2.5µA. The total amplifier current output requirements are, there- fore, ±27.5µA. Referring to the data given in Figure 5, we see that for an amplifier bias current of 20 µA the amplifier output current is ±40µA. This is obviously adequate and it is not necessary to change the amplifier bias current IABC. INVERTING INPUT V+ Q15 Q14 D7 D8 D6 D5 Q10 Q11 Q7 Q9 Q13 OUTPUT Q8 Q6 D4 Q12 Q3 - Q5 Q4 D2 D3 Q2 NON- INVERTING INPUT + AMPLIFIER BIAS CURRENT (ABC) V- D1 Q1 V- COMPLETE OTA CIRCUIT FIGURE 18. COMPLETE SCHEMATIC DIAGRAM SHOWING BIAS REGULATOR AND ONE OF THE THREE OPERATIONAL TRANSCONDUCTANCE AMPLIFIERS 8 15 AMPLIFIER 1 13 14 16 RABC 3 -6V RF RS - + 0.1 TO +6V RL 20k Ω 200k Ω 0.1 20k Ω 560k Ω INPUT ROFFSET <4M Ω -6V +6V 2.2M Ω 18k Ω +6V FIGURE 19. 20dB AMPLIFIER USING THE CA3060 CA3060 |
同様の部品番号 - CA3060 |
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同様の説明 - CA3060 |
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