A biasing circuit which provides biasing voltage for typical solid state output stage formed by complimentary Emitter Follower (hereinafter EF), complimentary Source Follower (hereinafter SF), or Complimentary Feedback Pair (hereinafter CFP), in an audio frequency power amplifier to establish stable biasing current comprising:
- a current sensing circuit which tracks the instantaneous conducting current in the complimentary power devices of said complimentary output stage and generates a complimentary voltage output pair with each voltage value corresponding to said output device current under tracking, respectively;
- wherein and hereinafter said complimentary device or voltage pair refers to the conjugative device pair of N and P type semiconductor devices or the conjugative voltage pair with one related to N type device and the other related to P type device, respectively;
- a complimentary voltage reference generator which generates a complimentary reference voltage pair which pairs with aforementioned complimentary voltage output pair to form a complimentary differential voltage pair to be used as the input of the complimentary differential amplifier mentioned hereinafter,
- a complimentary differential amplifier which takes aforementioned complimentary differential voltage pair as its input and generates an amplified differential output voltage which is only sensitive and related to the quiescent biasing current despite of the instant operation condition of the output transistor devices;
- wherein said complimentary differential amplifier contains only one amplification stage and said differential output voltage directly forms the input to the voltage multiplier mentioned hereinafter;
- a voltage multiplier which takes said voltage output of aforementioned complimentary differential amplifier as its input and generates an amplified output voltage which forms the biasing voltage and hence determines the quiescent biasing current of aforementioned complimentary output stage devices;
- a negative feedback scheme/loop which is formed through the connection of aforementioned current-to-voltage conversion circuit, complimentary reference voltage pair, complimentary differential amplifier, voltage multiplier and output devices;
- through which a desired quiescent biasing current is established and maintained in said complimentary output devices;
- wherein said feedback scheme/loop is constructed as described in following:
- said complimentary voltage output pair of said current sensing circuit and said complimentary reference voltage pair of said complimentary voltage reference generator form a complimentary differential input voltage pair which is connected to said input nodes of said complimentary differential amplifier;
- said differential output voltage nodes of said complimentary differential amplifier are connected to said input nodes of said voltage multiplier;
- said output nodes of said voltage multiplier are connected to the input nodes of said complimentary output power stage;
- through the formation of said feedback scheme/loop, the polarity of each connection is constructed in a way that only a negative (other than positive) feedback is formed within the entire loop when quiescent biasing current on output stage is considered as the variable in the feedback system.