Circuit, system and method for isolating a transducer from an amplifier in an electronic device

摘要

A circuit, device and method for controlling an output signal of an amplifier are provided. The output signal may be controlled through a first stage located before a digital to analog converter and/or a second stage located after it. The first stage boosts the digital signal to match with the full signal range of the converter. For the second stage, the circuit comprises: a first resistor coupled to an output of the amplifier in series, the first resistor having a resistance value Rs; a second resistor coupled to the first resistor in series, the second resistor having a resistance value Rp; and an output terminal for a transducer connected to the electronic device, the output terminal connected in parallel to the second resistor. In the circuit, the resistance values Rs and Rp are related by an inversely proportional relationship. The circuit provides an output signal at the output terminal having a noise floor that varies with an output level of the amplifier and a constant output impedance as seen from the transducer.

主权项

1. An electronic circuit for an output signal of an amplifier in an electronic device, comprising:
a speaker; a digital to analog converter (DAC); a microprocessor; a memory device storing instructions operable on the microprocessor to
sum a first output signal from a source input signal with a volume signal for a volume control signal for the source input signal to produce a resultant signal;boost the resultant signal to a boosted signal to use available headroom in the DAC, the boosted signal being within a threshold of a maximum digital input level for the DAC; andprovide the boosted signal to the DAC; an amplifier connected to an output of the DAC; and an interface circuit connected to an output of the amplifier and connected to the speaker, the interface circuit attenuating the output of the DAC to a second output signal representing a resultant volume level for the volume control signal, the interface circuit comprising
a first resistor coupled to the output of the amplifier in series, the first resistor having a resistance value Rs that limits current provided to the speaker from the electronic circuit;a second resistor coupled to the first resistor in series, the second resistor having a resistance value Rp to reduce a load impedance sensitivity for the speaker, where the Rs and Rp values are related by an inversely proportional relationship; andan output terminal for the speaker connected to the electronic device, the output terminal connected in parallel to the second resistor and providing the second output signal, wherein
the second output signal has a noise floor that varies with an output level of the amplifier.