Hi folks,
I'm working on designing a VCA around the CA3280 (actually ALFA AS3280). I've found some great resources like guest's paper on OTAs and a few others linked here. None, however, mention the exposed emitter pins or how I should think about taking advantage of them.
The only external reference to these I can find is an offhand remark in Serge's letter in Electronotes 113: "Due to parallel biasing of the internal PNP mirrors directly by IABC. it's not possible to inject a current into the available emitter pins, (unless an IABC of similar magnitude is also input)."
The Intersil CA3280 datasheet gives a terse statement in one of the examples, "Figure 10 shows a triangle wave to sine wave converter using the CA3280. Two 100kΩ resistors are connected between the differential amplifier emitters and V+ to reduce the current flow through the differential amplifier. This allows the amplifier to fully cut off during peak input signal excursions." The oscillator schematic in Figure 10, however, doesn't use the linearizing diodes at all, so it's hard to know how these would interact!
Should I use the I_D inputs *or* the emitters, but not both, for improving linearization? Or is there a way to use both in harmony?
I have been playing with the LTSPICE model of the 3280 from this post on the forum, but it doesn't show any distortion under basically any conditions, even with diodes disconnected. So it's hard to know how to design a theory of operation for these various controls.
I'm working on designing a VCA around the CA3280 (actually ALFA AS3280). I've found some great resources like guest's paper on OTAs and a few others linked here. None, however, mention the exposed emitter pins or how I should think about taking advantage of them.
The only external reference to these I can find is an offhand remark in Serge's letter in Electronotes 113: "Due to parallel biasing of the internal PNP mirrors directly by IABC. it's not possible to inject a current into the available emitter pins, (unless an IABC of similar magnitude is also input)."
The Intersil CA3280 datasheet gives a terse statement in one of the examples, "Figure 10 shows a triangle wave to sine wave converter using the CA3280. Two 100kΩ resistors are connected between the differential amplifier emitters and V+ to reduce the current flow through the differential amplifier. This allows the amplifier to fully cut off during peak input signal excursions." The oscillator schematic in Figure 10, however, doesn't use the linearizing diodes at all, so it's hard to know how these would interact!
Should I use the I_D inputs *or* the emitters, but not both, for improving linearization? Or is there a way to use both in harmony?
I have been playing with the LTSPICE model of the 3280 from this post on the forum, but it doesn't show any distortion under basically any conditions, even with diodes disconnected. So it's hard to know how to design a theory of operation for these various controls.
Statistics: Posted by kimballa — Sat Apr 27, 2024 10:25 pm
