NEDSP900 Development Board
27
Biasing
As the amplifiers are operating on a single supply rail they have no negative supply and therefore
Ground becomes the negative supply, in which case we create a ‘false’ ground rail by taking the Non-
Inverting input (IN +) of the Amplifier components, via R30, to half the rail voltage using R44 and R45.
This is a common practice. C39 then ensures that this new reference point is held steady and provides a
path for the A.C. signal component to Ground. So the Op- Amp sits with a supply voltage of +5V and is
biased such that the output sits as 2.5V. C49 is used to isolate this DC component from the follow on
stages.
Schematic Diagram of Balanced Audio Inputs
