I've read some of their blurb about hardening CMOS processes, do they also have bipolar tweaks?
In my experience the 5532 (basically the same but a dual, though mine tend to be TI rather than Philips) is one of the poor performers in respect of EMI. Just as one extreme example, I've tried it as an I/V out of an AD1955 (a fiendish source of broadband RF) with a very low value of feedback capacitor (<100pF). It sings like a bird even with no signal. Its EMI susceptibility could be the reason its got such a mixed reputation for sound quality.
Just because it says 5532 doesn't mean its the same inside. Signetics had some tweaks in their design and process. I don't have the databook anymore (30 yesrs+??) but I think there was some mention in it about applications in high RF environments like radio stations.
Mark Brasfield (Nationals specialist on those devices) told me that they had done a lot for emi hardening in those devices. All magic at the process level.
Mark Brasfield (Nationals specialist on those devices) told me that they had done a lot for emi hardening in those devices. All magic at the process level.
It is very good to have circuit's slew rate 50 - 100x higher than the highest possible dv/dt of the processed signal (re output).
Hi,
well, those voltage peaks run through the amplifier like wildfire, progressively overdriving the amplification stages, increasing the clipping and the resultant transients contain very high level of intermodulation distortion products. The kinds of amplifiers being discussed here are never far from reaching the SR limit, are rather below the limit all the time.
well, those voltage peaks run through the amplifier like wildfire, progressively overdriving the amplification stages, increasing the clipping and the resultant transients contain very high level of intermodulation distortion products. The kinds of amplifiers being discussed here are never far from reaching the SR limit, are rather below the limit all the time.
I don't understand this?
If you define slew rate per the linearity of the amp at high frequencies and high levels you will increased distortion and IM as you get closer to the SR threshold. If you are pushing the amp into internal saturation you will get latch-up and sticking on the output and saturation of the input as it tries to control the amp. Unless you have a digital source without an antialiasing filter its really unlikely you would approach either limit with audio you could listen to with any modern audio circuit.
1audio,
Why? We are talking about slew-rate limiting due to too small bandwidth, which is very common in feedback amplifiers. Slew-rate limiting depends on device properties (including configuration), topology and amplification factor. Obviously, high open-loop gain is the main culprit.
Slew rate does not equal bandwidth. (A common misconception) It's a large signal parameter that has mostly to do with the available drive in the vas/driver/output section. Its possible to have very high bandwidth with limited slew rate and you can find opamps that show tradeoffs both ways based on the same architecture and process.
Small signal bandwidth doesn't necessarily indicate full output bandwidth and slew rate is one of the links but other factors can affect the relationship as well.
Small signal bandwidth doesn't necessarily indicate full output bandwidth and slew rate is one of the links but other factors can affect the relationship as well.
Slew rate limiting is not due to bandwidth limiting. You can have a very small bandwidth with no slew rate limiting. Slew rate limiting is a large-signal phenomenon resulting from a signal rate of change that is larger than the maximum rate of change of an internal node. This happens for instance if the standing current in an amp stage is too small to charge and discharge an internal capacitor with large signals. But the amp will still be linear, no slew rate limiting, if you decrease signal level.
And it's not really very common in feedback amps; feedback amps with slew rate limiting are amps that are incompetently designed, and I would hope that after all these years we have learned to avoid that, high open loop gain or not. And we have. Except some designers that still live in the 60-ies 😉 .
jan didden
Last edited:
Hi Jan and 1audio,
slew-rate limiting occurs through any form of insufficiency, causing amplifier components to fail in handling the rate of change of the signal.
Amplifiers having a high open-loop gain and thereof poor bandwidth like operational amplifiers, particularly suffer from slew-rate limiting at high frequencies.
Aiming to avoid slew rate limiting completely is not necessarily always the best thing to do. However, a special thought should be given for the mechanisms creating high frequency transients because of their unpleasant nature.
slew-rate limiting occurs through any form of insufficiency, causing amplifier components to fail in handling the rate of change of the signal.
Amplifiers having a high open-loop gain and thereof poor bandwidth like operational amplifiers, particularly suffer from slew-rate limiting at high frequencies.
Aiming to avoid slew rate limiting completely is not necessarily always the best thing to do. However, a special thought should be given for the mechanisms creating high frequency transients because of their unpleasant nature.
I think it depends what you mean by "bandwidth".
For example, if an amplifier's open-loop small-signal frequency response rolls off above 5 kHz, it's closed-loop small-signal frequency response rolls off above 500 kHz, and it's maximum output power rolls off above 100 kHz, then the slew rate is directly related to the "100 kHz" number, which is often referred to as the "power bandwidth".
Those three numbers are independent of each other to a large extent.
For example, if an amplifier's open-loop small-signal frequency response rolls off above 5 kHz, it's closed-loop small-signal frequency response rolls off above 500 kHz, and it's maximum output power rolls off above 100 kHz, then the slew rate is directly related to the "100 kHz" number, which is often referred to as the "power bandwidth".
Those three numbers are independent of each other to a large extent.
Take Cdom as an example. If the least current available is 1mA and Cdom is 100 pF, the slew rate (SR) is less than 1mA/100pF=10 V/us. Increasing the current to 5 mA, increases the SR to 50 V/us. It has nothing to do with bandwidth of your amplifier. However you can calculate the max SR from your source (e.g a CD player) from its max bandwidth f (e.g 20 kHz) and amplitude (e.g 1 V) by finding the max SR as the max time derivate of the amplitude (e.g. SR = 0.13 V/us for our CD player).
Hi,
bandwidth represents the difference between the frequency limits of an amplifier, the range of frequencies over which an amplifier has a linear function according to some definition. Bandwidth needs to be very much wider than the intended operation frequency. I just stated that operational amplifiers suffer from slew-rate limiting because of poor bandwidth, in that context, there`s no need to assign further conditions. Slew-rate limiting was provided with, in my view, unambiguous meaning. I did not mean gain-bandwidth product, which is the product of the closed-loop gain and the -3 dB bandwidth.
bandwidth represents the difference between the frequency limits of an amplifier, the range of frequencies over which an amplifier has a linear function according to some definition. Bandwidth needs to be very much wider than the intended operation frequency. I just stated that operational amplifiers suffer from slew-rate limiting because of poor bandwidth, in that context, there`s no need to assign further conditions. Slew-rate limiting was provided with, in my view, unambiguous meaning. I did not mean gain-bandwidth product, which is the product of the closed-loop gain and the -3 dB bandwidth.
Attachments
Its common for consumer audio amps to have a frequency response of 300 KHz and a power bandwidth of 40 KHz. The reduced power bandwidth is due to slew rate limiting (or sometimes destruction of the output Zobel network). Your definition of bandwidth is inadequate to describe this situation.
As a designer of amplifiers that definition would get me into a lot of trouble. I need to know the requirements for the load to swing the full amplitude at the maximum frequency of the design. Its relatively easy to calculate back the necessary current at each stage to keep the amp linear at that maximum frequency working from the slew rate and peak currents required at each stage. But the calculation is independent of bandwidth and may (will) get you into trouble managing the phase margin at unity gain crossover if you don't watch all of the independent variables. At 500 KHz you find you need a lot of current in the input, vas, and driver stages, which may leave you with a lot of gain to manage and no phase margin to mange it.
As a designer of amplifiers that definition would get me into a lot of trouble. I need to know the requirements for the load to swing the full amplitude at the maximum frequency of the design. Its relatively easy to calculate back the necessary current at each stage to keep the amp linear at that maximum frequency working from the slew rate and peak currents required at each stage. But the calculation is independent of bandwidth and may (will) get you into trouble managing the phase margin at unity gain crossover if you don't watch all of the independent variables. At 500 KHz you find you need a lot of current in the input, vas, and driver stages, which may leave you with a lot of gain to manage and no phase margin to mange it.
- Status
- Not open for further replies.