Analogue attenuator controlled by binary switches - is used for volume and tone controls in stereo HI=FI systems using resistive ladder and divider chain

摘要

The analogue audio signal input (2) is connected to a resistive ladder network (4) with the steps connected via switching circuits (SN...S1) to the inverting input of an operational amplifier (6). Each switch is operated by the output of an individual comparator (Cn...C1). One input of each comparator is connected to a variable d.c. voltage source (9) which controls the attenuation factor, while the other input is connected to a fixed reference voltage supplied by a resistive divider chain (RVN...RV1). The level of the control voltage determines the number of switches operated and thus the attenuation provided by the ladder network. A feedback resistor (RN) on the output amplifier (6) provides a virtual earth input to the amplifier.