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Week #5: Discussion results

Week #5: Discussion results. OTAs. Group #33 Group member: Tianhao Han Ximeng Sun(Susie) Xing Cao(Star) Zhuoran Yang. LM 13600 was released in 1978 LM 13700 was released in 1997. Actually, w e do need a high voltage to control the OTA.

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Week #5: Discussion results

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  1. Week #5: Discussion results OTAs Group #33 Group member: TianhaoHan Ximeng Sun(Susie) Xing Cao(Star) Zhuoran Yang

  2. LM 13600 was released in 1978 LM 13700 was released in 1997 Actually, we do need a high voltage to control the OTA. • For manufacture, it is not hard to build an OTA with high input voltage. • Will not need a big area • Will not need a lot of extra cost Why don’t we make high input voltage OTA? The fact is……. All of the main product has released for over 30 years! And 30 years past, we still haven’t a product which is high input voltage OTA.

  3. LM 13600 VS LM 13700 • 13700 is next generation of 13600 • The price of LM13600 is about half the price as LM13700(not key point) • The input buffers of the 3700 and 3600 differ “in that the input bias currents (and hence their output DC levels) of the 3700 are independent of iabc which may result in performance superior to that of the 3600” • According to the LM datasheets, the buffer's input current range is 0.2 to 0.4uA for the 13600 and 0.5 to 2 uA for the 13700 • The Input offset voltages/changes in the 3600 have a slightly higher maximum rating (according to NJM datasheets, although they are the same according to LM datasheets)

  4. A actual lab A guy put together a voltage controlled current source for use at highcurrents (5 Amps) based on the desginat It uses a single supply op amp (OPA340 or OPA703) driving a low gate threshold logic level MOSFET (RFP30N06LE). Load connects between drain and power source. Current sense resistor from MOSFET source to ground with that junction feeding back through 10K to inverting input. Voltage control applied to non-inverting input.

  5. Because of the high current and the desire to minimize powerdissipation in the sense resistor and voltage drop across it, he isusing a 0.1 ohm sense resistor. This is resulting in the current not following the V=(current / 0.1 ohms) equation. He observes 0.725 A (expect 1 A) at 0.1V control voltage and 3.5 A (expect 5 A) at 0.5 V.These large errors are even present at low currents. Things arebetter for higher valued sense resistors. Reason----large errors? Stability? We need do a lab to figure out the result about high input voltage OTA.

  6. OTA used as: • Basic building block • OTA element simplifies designs of automatic gain control(AGC) amplifiers • Light-emitting diode(LED) driver circuits • Fast-pulse integrators • Control loops for capacitive sensors • Active filters

  7. Operational transconductance amplifier The major limiting factor with commercially available OTAs is the limited differential input voltage swing. An alternative is to use voltage attenuators and buffers at the input of existing OTAS. This technique can be used to obtain reasonable signal swings with all circuits discussed up to this point.

  8. Operational transconductanceamplifier Some disadvantages: • First, the circuit requires many more components. • Second, the finite bandwidth of the op amps will limit the frequency response of the OTA structures. • Finally, the attenuation of the input signal to the OTA causes a serious loss in dynamic range.

  9. Several reasons why there are no high input voltage OTAs.

  10. Reasons(Susie) • The part we add before original OTA. • Resister • BJT • The whole high-voltage OTA

  11. Schematic diagram

  12. Reasons(Susie) • The part we add before original OTA. • Resister • BJT • On-chip VS Off-chip • Accuracy • The whole high-voltage OTA • Power • Filter

  13. Question time.

  14. Thank you for your listening!

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