There is no upper limit for slew rate. Design criteria follows the anticipated load. For example, John Curl empirically determined that around 100V/uS is the max if no inductor is used in series with the load. This takes into account capacitive loading. Capacitive loading and output current capability determines what slew rate is viable, with or without inductor since high frequencies become a short circuit.
If feedback is employed, slew rate cannot be divorced from phase shift which determines square wave overshoot. What you want the output to look like under your chosen load conditions leads to the slew rate that is optimal for that design.
If feedback is employed, slew rate cannot be divorced from phase shift which determines square wave overshoot. What you want the output to look like under your chosen load conditions leads to the slew rate that is optimal for that design.
Hi Petr,
In the second edition of my book I go into considerable depth on both two-pole compensation (TPC) and Transitional Miller Compensation (TMC). They both do similar things and are similar in many ways, particularly in that the Miller feedback capacitor is split and a resistor connected to the joint. In TPC, the resistor usually goes to AC ground. In TMC, the resistor usually goes to the output.
TPC usually results in a closed loop overshoot. TMC does not. As far as the global feedback is concerned, TMC looks more like a classic single-pole rolloff.
Both techniques are quite effective if they are implemented properly and carefully. I tend to have a preference for TMC.
Cheers,
Bob
In the second edition of my book I go into considerable depth on both two-pole compensation (TPC) and Transitional Miller Compensation (TMC). They both do similar things and are similar in many ways, particularly in that the Miller feedback capacitor is split and a resistor connected to the joint. In TPC, the resistor usually goes to AC ground. In TMC, the resistor usually goes to the output.
TPC usually results in a closed loop overshoot. TMC does not. As far as the global feedback is concerned, TMC looks more like a classic single-pole rolloff.
Both techniques are quite effective if they are implemented properly and carefully. I tend to have a preference for TMC.
Cheers,
Bob
I suggest you read my paper "A MOSFET Power Amplifier with Error Correction at
CordellAudio.com - A MOSFET Power Amplifier with Error Correction
That 50-watt amplifier achieved slew rate of 300 V/us while maintaining a virtually perfect 10 kHz square wave and THD-20 of 0.001% up to full power.
Cheers,
Bob
Hi Bob!
Bob, I read this article once. It used the Hawksford OPS. Industrial amplifiers were produced according to this scheme?
A number of prestigious Electrocompaniet amplifiers have been released based on Othal's ideas.
Curl inspired a number of Parasound amplifiers and more ...
And what specific brands of amplifiers are released according to your ideas or circuits? And where can you find independent tests of your amplifiers?
best regards
Petr
Bob, I read this article once. It used the Hawksford OPS. Industrial amplifiers were produced according to this scheme?
A number of prestigious Electrocompaniet amplifiers have been released based on Othal's ideas.
Curl inspired a number of Parasound amplifiers and more ...
And what specific brands of amplifiers are released according to your ideas or circuits? And where can you find independent tests of your amplifiers?
best regards
Petr
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I have read the paper. It is a notable achievement. My comment does not contest that. However, I make differentiation between paper specification and real world use. Ie. How many amps/uS is required for 300V/uS into 8R in parallel with 0.1uF?. If an inductor is present, does the load see 300V/uS?
Bob:
“Most of Otala's claims concerning TIM, IIM and PIM were disproven long ago. Large amounts of negative feedback do not increase these distortions in a properly designed amplifier. These distortions are objectively measurable and have been shown to be usually in fact smaller in amplifiers with large amounts of negative feedback.”
Bob, I have not seen a single serious article that would refute PIM distortion in amplifiers. If anyone has written such articles, then most likely they measured the wrong thing. For example, there is an article by Cherry [Cherry EM Amplitude and Phase of Intermodulation Distortion. -JAES, 1983, 31, N 5, p. 238-304] in which the author theoretically substantiated the occurrence of phase distortion.
The author of another article (??????? ???????? ???????? ? ???????? ????????????? ?????????? ???????? ??????? A.M. Likhnitsky The reasons for the audible differences in the sound transmission of audio amplifiers) used a standard detonation meter to measure the detonation of sound in tape recorders and showed that a detonation level of 0.6% occurs in a typical audio amplifier, which is known [Saka I H. Perceptibility of Wow and Flutter. - JAES, 1970, 18, N * 3, p. 290-298], is ten times higher than the threshold of noticeability of this type of distortion and two times - the permissible value of these distortions in cassette recorders of the third class.
“Most of Otala's claims concerning TIM, IIM and PIM were disproven long ago. Large amounts of negative feedback do not increase these distortions in a properly designed amplifier. These distortions are objectively measurable and have been shown to be usually in fact smaller in amplifiers with large amounts of negative feedback.”
Bob, I have not seen a single serious article that would refute PIM distortion in amplifiers. If anyone has written such articles, then most likely they measured the wrong thing. For example, there is an article by Cherry [Cherry EM Amplitude and Phase of Intermodulation Distortion. -JAES, 1983, 31, N 5, p. 238-304] in which the author theoretically substantiated the occurrence of phase distortion.
The author of another article (??????? ???????? ???????? ? ???????? ????????????? ?????????? ???????? ??????? A.M. Likhnitsky The reasons for the audible differences in the sound transmission of audio amplifiers) used a standard detonation meter to measure the detonation of sound in tape recorders and showed that a detonation level of 0.6% occurs in a typical audio amplifier, which is known [Saka I H. Perceptibility of Wow and Flutter. - JAES, 1970, 18, N * 3, p. 290-298], is ten times higher than the threshold of noticeability of this type of distortion and two times - the permissible value of these distortions in cassette recorders of the third class.
Hi Petr,
PIM DOES exist, and I built a piece of test equipment for measuring very small amounts of if. See a paper on PIM on my web page. However, people misunderstand the difference between PIM existing and what causes PIM and by how much. What is wrong with Otala's assertions is not that these distortions exist, but rather that negative feedback exacerbates PIM. I have shown both mathematically and by measurement that, in most cases, NFB does not exacerbate PIM.
PIM goes way back earlier than Otala's pepers on it. It is called differential gain and phase, and was especially a prominent issue in NTSC color TV transmission. It is simply the fact that phase shift through an amplifier can be dependent on the amplitude of the signal, just as the incremental gain of an amplifier can be dependent on the amplitude of the signal. The latter is the basis for the SMPTE IM test. The latter is just Amplitude Intermodulation Distortion (AIM).
PIM occurs in amplifiers even without any negative feedback. For example, the nonlinear base-collector junction capacitance of a transistor can modulate the bandwidth of that stage. Whenever bandwidth is modulated as a function of signal amplitude, PIM will result.
In a negative feedback amplifier, anything that modulates the open loop gain as a function of signal amplitude modulates the closed loop gain and thus causes PIM. If the input stage gain is modulated as a function of signal amplitude, PIM will occur, but so will AIM. Any PIM will always be accompanied by other distortions.
Cheers,
Bob
PIM DOES exist, and I built a piece of test equipment for measuring very small amounts of if. See a paper on PIM on my web page. However, people misunderstand the difference between PIM existing and what causes PIM and by how much. What is wrong with Otala's assertions is not that these distortions exist, but rather that negative feedback exacerbates PIM. I have shown both mathematically and by measurement that, in most cases, NFB does not exacerbate PIM.
PIM goes way back earlier than Otala's pepers on it. It is called differential gain and phase, and was especially a prominent issue in NTSC color TV transmission. It is simply the fact that phase shift through an amplifier can be dependent on the amplitude of the signal, just as the incremental gain of an amplifier can be dependent on the amplitude of the signal. The latter is the basis for the SMPTE IM test. The latter is just Amplitude Intermodulation Distortion (AIM).
PIM occurs in amplifiers even without any negative feedback. For example, the nonlinear base-collector junction capacitance of a transistor can modulate the bandwidth of that stage. Whenever bandwidth is modulated as a function of signal amplitude, PIM will result.
In a negative feedback amplifier, anything that modulates the open loop gain as a function of signal amplitude modulates the closed loop gain and thus causes PIM. If the input stage gain is modulated as a function of signal amplitude, PIM will occur, but so will AIM. Any PIM will always be accompanied by other distortions.
Cheers,
Bob