| 摘要 |
The common-mode bias voltage VgDC in a class AB push-pull amplifier is adjusted by a closed-loop control circuit which minimises distortion in the crossover region. Sense resistors 140 and 142 provide voltages Vs1 and Vs2 proportional to the currents in the FETs Q1 and Q2. These voltages are converted to currents in a pair of non-linear bipolar transistor circuits (figure 6) and these currents are summed to provide an output signal which is substantially invariant with signal voltage when the bias is optimal for minimum crossover distortion (706, figure 7), but which is respectively too high (704, figure 7) or too low when the bias voltage is too high or too low. The sum output of the nonlinear circuit may be compared with a reference and the error signal integrated to provide the bias control signal. The nonlinear circuit ensures that the bias control circuit is sensitive only in the crossover region and is insensitive to the amplitude of the input signal Vsig |
