Negative audio signal voltage protection circuit and method for audio ground circuits

摘要

Self-grounded circuitry (10) includes a signal channel conducting an output voltage (VOUT1). A charge pump (2) powered by a reference voltage (VDD) produces a control voltage (VCP). The control signal is at a low level if the reference voltage is low and is boosted to a high level if the reference voltage is high. A ground switch circuit (15) includes a depletion mode transistor (MP1) having a source coupled to the output voltage, a gate coupled to the control voltage, and a drain coupled to ground. The transistor includes a well region (4-1) and a parasitic substrate diode (D3-1). A negative voltage protection circuit (17-1) includes a depletion mode first protection transistor (MP3-1) having a drain coupled to the well region, a source coupled to a source of a depletion mode second protection transistor (MP4-1) having a drain coupled to the output voltage, the first and second protection transistors each having a gate coupled to the control voltage, and also includes a diode (MN1) coupled to charge the well region from the control voltage conductor to prevent distortion of the output voltage.

主权项

1. Self-grounded circuitry comprising:
(a) a first signal channel conducting a first output signal on a first output conductor; (b) a charge pump powered by a first reference voltage and producing a control voltage signal on a control conductor, the control voltage signal having a relatively low value if the first reference voltage is at a relatively low level and having a relatively high value if the first reference voltage is at a relatively high level; (c) a ground switch circuit including a first depletion mode transistor having a source coupled to the first output conductor, a gate coupled to receive the control voltage signal, and a drain coupled to a second reference voltage, the first depletion mode transistor having a first well region, a first parasitic diode including a PN junction between the source and the first well region, a second parasitic diode including a PN junction between the drain and the first well region, and a third parasitic diode including a PN junction between the first well region and a substrate ajoining the first well region; and (d) a first negative voltage protection circuit including
1) a first depletion mode protection transistor having a drain coupled to the first well region, a source coupled to a source of a second depletion mode protection transistor having a drain coupled to the first output conductor, the first and second depletion mode protection transistors each having a gate coupled to the control conductor, well regions of the first and second depletion mode protection transistors being connected to their sources, respectively, and2) a level-shifting circuit coupled between the first well region and the control conductor.