On Wed, Jun 9, 2010 at 3:05 PM, <fons@xxxxxxxxxxxxxxx> wrote: >> But a wide-bandwidth op-amp is going to be >> intrinsically noisier.... and a quiet op-amp is going to be >> intrinsically slower, > > No, there's no such simple relation. Actually there is a relationship, and it is certainly not simple. However the generality holds, mostly because when you get down to it a fast device achieves speed through either size, or high-current. High-current induces one kind of noise, and small device geometries induce another; field-effect, it's own, alongside material device physics, temperatures, etc... For example one might prefer FET or MosFet for linearity and gain-bandwidth linearity, but they're noisy. Ultimately it comes down to gain-bandwidth, which is nonlinear in low-noise Bipolar Junction-based opamps like you'd normally use in audio: http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_3.pdf http://focus.ti.com.cn/cn/lit/an/sloa051a/sloa051a.pdf "Selecting High-Speed Operational Amplifiers Made Easy" ........... Although no op amp is ideal, modern processing techniques yield devices that come close, at least in some parameters. This is by design. In fact, different op amps are optimized to be close to ideal for some parameters, while other parameters for the same op amp may be quite ordinary. It is a trade-off. Some parameters can be improved, but only at the expense of others. It is the designer’s function to select the op amp that is closest to ideal in ways that matter to the application, and to know which parameters can be discounted or ignored. [...] Op amp design is a series of trade-offs and an improvement in one parameter is always accompanied by degradation of others. This is certainly the case with current-feedback amplifiers where, to a degree, dc performance has been sacrificed to gain speed. ............. -- Niels http://nielsmayer.com _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
