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addition of these diodes increases the linearity of the input stage by a factor of 4. That is, using the diodes, the signal distortion level at 80 mV of differential input is the same as that of the simple differential amplifier at a differential input of 20 mV. Second, the action of the biased diodes offsets much of the temperature sensitivity of the OTA's transconductance.
158:(VCCS). Three types of OTAs are single-input single-output, differential-input single-output, and differential-input differential-output (a.k.a. fully differential), however this article focuses on differential-input single-output. There may be an additional input for a current to control the amplifier's
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terminal. These additions make two substantial improvements to the OTA. First, when used with input resistors, the diodes distort the differential input voltage to offset a significant amount of input stage non linearity at higher differential input voltages. According to
National Semiconductor, the
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A second improvement is the integration of an optional-use output buffer amplifier to the chip on which the OTA resides. This is actually a convenience to a circuit designer rather than an improvement to the OTA itself; dispensing with the need to employ a separate buffer. It also allows the OTA to
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terminal (shown in the diagram) nor the diodes (shown adjacent to it). They were all added in later versions. As depicted in the diagram, the anodes of the diodes are attached together and the cathode of one is attached to the non inverting input (Vin+) and the cathode of the other to the inverting
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at higher differential input voltages due to the characteristics of the input stage transistors. In the early devices, such as the CA3080, the input stage consisted of two bipolar transistors connected in the differential amplifier configuration. The transfer characteristics of this connection are
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The OTA is usually used "open-loop"; without negative feedback in linear applications. This is possible because the magnitude of the resistance attached to its output controls its output voltage. Therefore, a resistance can be chosen that keeps the output from going into
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Schematic symbol for an OTA with differential input. Like the standard operational amplifier, it has both inverting (−) and noninverting (+) inputs; power supply lines (V+ and V−); and a single output. Unlike the traditional op-amp, it has two additional biasing inputs,
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approximately linear for differential input voltages of 20 mV or less. This is an important limitation when the OTA is being used open loop as there is no negative feedback to linearize the output. One scheme to improve this parameter is mentioned below.
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634:{\displaystyle G_{\mathrm {voltage} }={V_{\mathrm {out} } \over V_{\mathrm {in+} }-V_{\mathrm {in-} }}=R_{\mathrm {load} }\cdot g_{\mathrm {m} }}
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Variation of input and output impedance, input bias current and input offset voltage with the transconductance control current I
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Data Sheet for LM 13700 – Graph of
Distortion v. Differential Input Voltage (National Semiconductor, June 2004) p. 6.
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In the ideal OTA, the output current is a linear function of the differential input voltage, calculated as follows:
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An example of a chip combining both of these features is the
National Semiconductor LM13600 and its successor, the
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slew-rate and bandwidth improvement of the CMOS OTA based on the frequency overdrived current mirror (archive)
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to ground, the OTA's output voltage is the product of its output current and its load resistance:
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As with the standard op-amp, practical OTA's have some non-ideal characteristics. These include:
338:{\displaystyle I_{\mathrm {out} }=(V_{\mathrm {in+} }-V_{\mathrm {in-} })\cdot g_{\mathrm {m} }}
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be used as a traditional op-amp, if desired, by converting its output current to a voltage.
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785:"LM13700 Dual Operational Transconductance Amplifiers With Linearizing Diodes and Buffers"
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The transconductance of the amplifier is usually controlled by an input current, denoted I
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The voltage gain is then the output voltage divided by the differential input voltage:
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476:{\displaystyle V_{\mathrm {out} }=I_{\mathrm {out} }\cdot R_{\mathrm {load} }}
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The first commercially available integrated circuit units were produced by
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input (Vin−). The diodes are biased at the anodes by a current (I
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A Short
Discussion of the Operational Transconductance Amplifier (OTA)
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aren't directly implementable with OTAs. However, OTAs can implement
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Discrete OTAs for Synth-DIY & Elektor-Formant-Upgrades (archive)
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proportional to its input voltage. Thus, it is a voltage controlled
120:
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Comparison of
Operational Transconductance Amplifiers (archive)
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18:
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Reducing voltage offset of the integrated CMOS OTA (archive)
768:(Howard W. Sams -Bobbs-Merrill First Ed. 1974) p. 440
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These differences mean the vast majority of standard
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https://www.ijsr.net/archive/v2i3/IJSRON2013566.pdf
49:. Unsourced material may be challenged and removed.
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196:while a standard operational amplifier outputs a
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184:differential input stage and may be used with
684:Earlier versions of the OTA had neither the I
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668:Temperature sensitivity of transconductance.
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109:Learn how and when to remove this message
58:"Operational transconductance amplifier"
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140:operational transconductance amplifier
790:. Texas Instruments. 15 December 2015
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373:If the load is just a resistance of
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393:{\displaystyle R_{\text{load}}}
188:. But the OTA differs in that:
34:needs additional citations for
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226:variable frequency oscillators
222:voltage-controlled oscillators
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726:– converts current to voltage
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230:voltage-controlled resistors
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900:Linear integrated circuits
853:MAX 436 (obsolete product)
849:MAX 435 (obsolete product)
218:voltage-controlled filters
180:, the OTA also has a high
845:CA3080 (obsolete product)
652:Non-ideal characteristics
232:, and voltage-controlled
812:(Hayden, 1980) p. 40-41.
724:Transimpedance amplifier
234:variable gain amplifiers
680:Subsequent improvements
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192:The OTA outputs a
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16:Electrical circuit
810:IC Array Cookbook
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99:December 2006
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54:Find sources:
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32:This article
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808:Jung, W.G.,
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792:. Retrieved
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660:Input stage
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41:Please help
36:verification
33:
889:Categories
843:Examples:
794:26 January
206:saturation
69:newspapers
617:⋅
584:−
569:−
450:⋅
321:⋅
312:−
297:−
182:impedance
148:amplifier
713:See also
146:) is an
857:LM13700
770:et seq.
707:LM13700
366:is the
198:voltage
194:current
152:current
83:scholar
865:OPA861
861:OPA860
754:CA3080
348:where
224:(e.g.
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56:
788:(PDF)
731:Notes
130:and I
90:JSTOR
76:books
796:2016
695:bias
691:bias
686:bias
386:load
138:The
132:bias
62:news
673:abc
646:abc
360:in−
353:in+
228:),
167:RCA
162:.
144:OTA
128:abc
45:by
891::
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593:=
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498:G
468:d
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459:l
454:R
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429:=
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412:V
382:R
364:m
357:V
350:V
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276:(
273:=
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106:(
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97:(
87:·
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