Issue 03 of 2016_11_12
INTRODUCTION
There have been many game-changers in the history of operational amplifiers (opamps): µA709, µA741, LM358, TL072 (see link below). I'm wondering if the Texas Instruments OPAx192 family isn't the latest. I've been itching to try one out since the data sheet was released around 2013, but even though the devices are now freely available, I don't have a workshop at the moment. But I have done quite a few paper designs using the OPAx192 now, and have found that the opamp's characteristics have greatly simplified the design and enhanced the theoretical performance.
GO-TO OPAMP
The LM358 has been the low-cost, go-to dual opamp for years. The functional equivalent would be the OPA2192, which would have a vastly improved performance, with the exception of low voltage operation: 4.5V versus 3V for the LM358.
WHAT IS SO GOOD ABOUT THE OPAx192?
Going by the datasheet, this operational amplifier is remarkable, in fact, practically perfect and opens up a whole raft of circuit design possibilities. It should also help students/newbees, because many of the shortcomings of the common 741 types, tend to cloud the issue when an actual circuit is built and tested. Surprisingly, in spite of the specification, the OPAx192 isn't too expensive either: Mouser has them at a one-of price of around $2.00US/£2.00UK, and this will probably drop when the OPAx192 family has been on the market a bit longer. http://uk.mouser.com/search/refine.aspx?Ntk=P_MarCom&Ntt=152100822
PERFORMANCE
Here are the main parameters from the datasheet (see link below) that make this operational amplifier so exceptional, especially the extremely low input offset voltage and current. Before this you might have got some of these advanced features in one chip, but what makes this chip unique is that it has them all:
• Wide Supply Rails: ±2.25 V to ±18 V, +4.5 V to +36 V
• High output current (±65 mA)
• Plus rail +100mV and minus rail -100mV Input Voltage Range
• Rail-to Rail Output Voltage
• Low Quiescent Current: 1 mA per Amplifier
• Differential Input Voltage Range to Supply Rails
• Wide Bandwidth: 10 MHz Gain Bandwidth Product
• High Slew Rate: 20 V/μs
• High Capacitive Load Drive Capability: 1 nF
• Unity Gain Stable
• Low Input Offset Voltage: ±5 μV (not a typo)
• Low input Offset Voltage Drift: ±0.2 μV/°C
• Low Input Bias Current: ±5 pA (not a typo)
• Available in single (OPA192), dual (OPA292), and quad (OPA492) versions
• Spice model available on TI site
LIMITATIONS
One slight downside is that the OPAx92 is only available in surface mount, but there's always the option of mounting the surface mount package on a DIL converter/header for experimenting.
Also, the rail-to-rail input relies on two complimentary differential amplifiers in parallel at the input. The bottom differential amplifier handles all input signals from -100mV below the negative supply rail to approximately 2.5V below the positive supply rail, where the top differential amplifier takes over. This gives a slight discontinuity in the transfer function at the change-over point which probably wouldn't be significant at DC and low frequencies but would be an area to avoid for higher frequencies and HiFi audio. Also when operating in the top differential amplifier input voltage range the performance of the OPAx92 is slightly compromised.
RELATED OPAMPS
The OPAx191 is a low noise version
The OPAx197 has a relaxed input off-set voltage and is, thus, lower cost.
The OPAx171 has a similar architecture to the OPAx192 but has a much lower power consumption, with subsequent lower frequency response and output current drive capability. The OPAx171 can also operate from a lower supply voltage: 2.7V as opposed to 4.5V
LINKS
(1) Opamp milestones: http://corphist.computerhistory.org/corphist/documents/doc-4803f5a67ccc3.pdf
(2) OPAx92 family datasheet: http://www.ti.com/lit/ds/symlink/opa192.pdf
(3) OPAx191 family datasheet: http://www.ti.com/lit/ds/symlink/opa191.pdf
(4) OPAx197 family datasheet: http://www.ti.com/lit/ds/symlink/opa197.pdf
(5) OPAx171 family datasheet: http://www.ti.com/lit/ds/symlink/opa171.pdf
(6) LM358 datasheet: http://www.ti.com/lit/ds/symlink/lm158-n.pdf
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