Current Injection describes a method of shortening the signal path and improves the sound quality and measurement specs significantly. The effective simplicity of Current Injection requires a non-feedback-loop amplifier. While Current Injection replaces the voltage amplifier LEF guarantees best performance of the current amplifier with low THD. Both technologies complement each other and overcome the limitations of traditional circuitry to a better standard of music reproduction.
This essay intends to give an understanding of the basic idea of Current Injection.
As an example a digital / analogue converter output stage is used.
shows a simplified traditional connection of a current output digital / analogue converter to an analogue amplifier stage. The current to voltage conversion as well as the first filter pole is done through a feedback loop which is a questionable solution concerning dynamic performance.
Basically it should be understood that any normal amplifier concept replaces the original signal by a “copy”. No copy is as good as the original and the more the original music signal is “copied”, the more the result differs from the original.
The input signal “moves” the voltage amplifier stages in the OP-amplifier (at least 2 voltage amplifier stages within one OP-amplifier). Each stage delivers a “copy” of the original signal and finally the current buffer stage generates a further “copy”. Because all these copies are certainly far from being perfect a negative feedback loop is used for reducing the signal degradation—this method is not free of side effects.
Due to the filtering requirements of a digital audio device at least 2 OP-amplifier are required, which adds a further “copy session”. In total the traditional solution requires at least 6 copies. A proper handling of balanced signals as shown in Fig. 1b further increases the quantity of amplifier stages within the signal path. In case differential DAC signal proceeding is required for XLR output as well, the quantity of amplifier stages increases again.