Constant output pulse amplifier in cordless telephone handset - uses variable amplifier in feedback from comparator reference input

摘要

The amplifier for received i.r. pulse phase modulated speech signals is extended to make these largely independent from prevailing receiving conditions. The output (SM) of a photoelectric transducer is applied to a variable amplifier (VR) which responds to a regulator (RE) voltage in an inverse proportional sense. The amplified output (PV) is passed partly to a comparator (K01), partly to the non-inverting input of a differential amplifier (K02) which combined with rectifier (GL) and low pass filter (TP) produces a regulator voltage (UR). The same fulfills two functions. By feedback to the variable amplifier it tends to keep the pulse peak output level constant and the comparator output dependent on the setting of a potentiometer (RS) remains at the set level. If, however, the received signal becomes so weak that amplifier VR can no longer attain the regulated level, the second function of the regulator voltage (UR) comes into play in that it lowers the comparator level with which the pulse peaks are compared.