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MC1494 Datenblatt(PDF) 10 Page - ON Semiconductor |
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MC1494 Datenblatt(HTML) 10 Page - ON Semiconductor |
10 / 16 page MC1494 10 MOTOROLA ANALOG IC DEVICE DATA –V2 10 9 10 + + 15 5 14 2 3 – + 11 12 30 k 62 k 78 +15 V –15 V P4 50 k 22 k 10 pF MC1456 –15 V +15 V 4 7 10 pF 510 V + MC1494 13 6 13 4 2 16 k 51 k 20 k P1 20 k Input Offset P3 Output Offset 6 VO = Figure 21. MC1494 Squaring Circuit This shows that all error terms can be eliminated with only three adjustment potentiometers, eliminating one of the input offset adjustments. For instance, if the “X” input offset adjustment is eliminated, ∈x is determined by the internal offset (Viox) but ∈y is adjustable to the extent that the (∈x + ∈y) term can be zeroed. Then the output offset adjustment is used to adjust the Voo term and thus zero the remaining error terms. An AC procedure for nulling with three adjustments is: A. AC Procedure: 1. Connect oscillator (1.0 kHz, 15 Vpp) to input. 2. Monitor output at 2.0 kHz with tuned voltmeter and adjust P4 for desired gain ( Be sure to peak response of voltmeter). 3. Tune voltmeter to 1.0 kHz and adjust P1 for a minimum output voltage. 4. Ground input and adjust P3 (output offset) for 0 Vdc out. 5. Repeat steps 1 through 4 as necessary. B. DC Procedure: 1. Set VX = VY = 0 V and adjust P3 (output offset potentiometer) such that VO = 0 Vdc. 2. Set VX = VY = 1.0 V and adjust P1 (Y input offset potentiometer) such that the output voltage is – 0.100 V. 3. Set VX = VY = 10 Vdc and adjust P4 (load resistor) such that the output voltage is –10 V. 4. Set VX = VY = –10 Vdc and check that VO = –10 V. 5. Repeat steps 1 through 4 as necessary. Divide Divide circuits warrant a special discussion as a result of their special problems. Classic feedback theory teaches that if a multiplier is used as a feedback element in an operational amplifier circuit, the divide function results. Figure 22 illustrates the theoretical simplicity of such an approach and a practical realization is shown in Figure 23. The characteristic “failure” mode of the divide circuit is latch–up. One way it can occur is if VX is allowed to go negative, or in some cases, if VX approaches zero. Figure 22 illustrates why this is so. For VX > 0 the transfer function through the multiplier is noninverting. Its output is fed to the inverting input of the op amp Thus, operation is in the negative feedback mode and the circuit is DC stable. + + + + – VZ – KVX VY VX MC1494 VO VZ = –KVXVY or VO = –VZ KVX + Figure 22. Basic Divide Circuit Using Multiplier VY Should VX change polarity, the transfer function through the multiplier becomes inverting, the amplifier has positive feedback and latch–up results. The problem resulting from VX being near zero is a result of the transfer through the multiplier being near zero. The op amp is then operating with a very high closed–loop gain and error voltages can thus become effective in causing latch–up. The other mode of latch–up results from the output voltage of the op amp exceeding the rated common mode input voltage of the multiplier. The input stage of the multiplier becomes saturated, phase reversal results, and the circuit is latched up. The circuit of Figure 23 protects against this happening by clamping the output swing of the op amp to approximately ± 10.7 V. Five percent tolerance, 10 V zeners are used to assure adequate output swing but still limit the output voltage of the op amp from exceeding the common mode input range of the MC1494. Setting up the divide circuit for reasonably accurate operation is somewhat different from the procedure for the multiplier itself. One approach, however, is to break the feedback loop, null out the multiplier circuit, and then close the loop. |
Ähnliche Teilenummer - MC1494 |
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Ähnliche Beschreibung - MC1494 |
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