This interesting circuit found in American documentation generates a busy signal, without you having to take the phone off the hook if you do not want to answer. The components used are common.
This low noise preamplifier has a gain of 19 dB in the 30 MHz band. The circuit is from the 80s....
The purpose of the strobe circuit in this sensor amplifier is to reduce consumption. The circuit is...
The amplifier gain shown in the figure is given by R1. The circuit is valid for other photodiodes and is...