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MC1494P Folha de dados(PDF) 11 Page - ON Semiconductor |
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MC1494P Folha de dados(HTML) 11 Page - ON Semiconductor |
11 / 16 page MC1494 11 MOTOROLA ANALOG IC DEVICE DATA Figure 23. Practical Divide Circuit 30 k 62 k 11 12 7 8 RL 50 k 22 k 10 pF 14 1 2 3 6 VO +15 V –15 V MC1494 MC1741CP1 1N5240A (10 V) or Equivalent VO = –10 VZ VX 0 < VX < +10 V –10 V ≤ VZ ≤ +10 V –15 V +15 V P2 20 k P3 50 k P1 20 k 2 10 9 6 3 16 k + + + – VZ 515 13 4 10 pF 510 10 pF 510 4 7 VX A simpler approach, since it does not involve breaking the loop (thus making it more practical on a production basis), is: 1. Set VZ = 0 V and adjust the output offset potentiometer (P3) until the output voltage (VO) remains at some (not necessarily zero) constant value as VX is varied between +1.0 V and +10 V. 2. Maintain VZ at 0 V, set VX at +10 V and adjust the Y input offset potentiometer (P1) until VO = 0 V. 3. With VX = VZ, adjust the X input offset potentiometer (P2) until the output voltage remains at some (not necessarily –10 V) constant value as VZ = VX is varied between +1.0 V and +10 V. 4. Maintain VX = VZ and adjust the scale factor potentiometer (RL) until the average value of VO is –10 V as VZ = VX is varied between +1.0 V and +10 V. 5. Repeat steps 1 through 4 as necessary to achieve optimum performance. Users of the divide circuit should be aware that the accuracy to be expected decreases in direct proportion to the denominator voltage. As a result, if VX is set to 10 V and 0.5% accuracy is available, then 5% accuracy can be expected when VX is only 1.0 V. In accordance with an earlier statement, VX may have only one polarity (positive) while VZ may be either polarity. KVO2 = –VZ or VO = |VZ| K VZ ≤ 0 V Figure 24. Basic Square Root Circuit + + + – VZ – KVO2 X MC1494 VO + Square Root A special case of the divide circuit in which the two inputs to the multiplier are connected together results in the square root function as indicated in Figure 24. This circuit too may suffer from latch–up problems similar to those of the divide circuit. Note that only one polarity of input is allowed and diode clamping (see Figure 25) protects against accidental latch–up. This circuit too, may be adjusted in the closed–loop mode: 1. Set VZ = –0.01 Vdc and adjust P3 (output offset) for VO = 0.316 Vdc. 2. Set VZ to –0.9 Vdc and adjust P2 (“X” adjust) for VO = +3.0 Vdc. 3. Set VZ to –10 Vdc and adjust P4 (gain adjust) for VO = +10 Vdc. 4. Steps 1 through 3 may be repeated as necessary to achieve desired accuracy. NOTE: Operation near 0 V input may prove very inaccurate, hence, it may not be possible to adjust VO to zero but rather only to within 100 mV to 400 mV of zero. AC APPLICATIONS Wideband Amplifier with Linear AGC If one input to the MC1494 is a DC voltage and a signal voltage is applied to the other input, the amplitude of the output signal can be controlled in a linear fashion by varying the DC voltage. Hence, the multiplier can function as a DC coupled, wideband amplifier with linear AGC control. In addition to the advantage of linear AGC control, the multiplier has three other distinct advantages over most other types of AGC systems. First, the AGC dynamic range is theoretically infinite. This stems from the basic fact that with 0 Vdc applied to the AGC, the output will be zero regardless of the input. In practice, the dynamic range is limited by the ability to adjust the input offset adjust potentiometers. By using cermet multi–turn potentiometers, a dynamic range of 80 dB can be obtained. The second advantage of the multiplier is that variation of the AGC voltage has no effect on the signal handling capability of the signal port, nor does it alter the input impedance of the signal port. This feature is particularly important in AGC systems which are phase sensitive. A third advantage of the multiplier is that the output voltage swing capability and output impedance are unchanged with variations in AGC voltage. |
Nº de peça semelhante - MC1494P |
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Descrição semelhante - MC1494P |
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