You can use a low-cost PC sound card as an analog-function generator by controlling the PC with the program `SoundArb.` [To obtain SoundArb, download di2409setup.exe, a 1.06-Mbyte self-extracting installation program.] The program generates standard waveforms, noise, and arbitrary waveforms. The program reads arbitrary waveforms from simple ASCII text files consisting of white-space-separated numbers. You can use a program such as Mathcad to create such files.
Elektor (blog) This is ideal for products in which boards are mounted at different angles to each other and there is no requirement for ongoing flexibility. The circuit board only needs to be bent into the desired shape once, during assembly
EDN.com Some ideal op amp configurations assume that the feedback resistors exhibit perfect matching. In practice, resistor non-idealities can affect parameters such as common mode rejection ratio (CMRR), harmonic distortion and stability.