Negative Audio Signal Voltage Protection Circuit and Method for Audio Ground Circuits

A method for preventing distortion of an output signal caused by ground switch circuitry in a self-grounding switch circuit, the method comprising:

• (a) providing the output signal on an output conductor;
• (b) operating a charge pump powered by a first reference voltage to produce 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) applying the control voltage signal to a gate of a depletion mode ground switch transistor having a source coupled to the output conductor and a drain coupled to a second reference voltage, the depletion mode ground switch transistor having a well region, a first parasitic diode including a PN junction between the source and the well region, a second parasitic diode including a PN junction between the drain and the well region, and a third parasitic diode including a PN junction between the well region and a substrate ajoining the well region;
• and
• (d) coupling the well region to a drain of a first depletion mode protection transistor having a drain coupled to the well region, a source coupled to a source of a second depletion mode protection transistor having a drain coupled to the output conductor, coupling a gate of each of the first and second depletion mode protection transistors to the control conductor, coupling a level-shifting circuit between the well region and the control conductor, and coupling well regions of the first and second depletion mode protection transistors to their sources, respectively.

Circuitry for preventing distortion of an output signal caused by ground switch circuitry in an AC signal circuit, comprising:

• (a) means for providing the AC output signal on an output conductor;
• (b) a charge pump powered by a first reference voltage to produce 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 second reference voltage is at a relatively high level;
• (c) means for applying the control voltage signal to a gate of a depletion mode ground switch transistor having a source coupled to the output conductor and a drain coupled to a second reference voltage, the depletion mode ground switch transistor having a well region, a first parasitic diode including a PN junction between the source and the well region, a second parasitic diode including a PN junction between the drain and the well region, and a third parasitic diode including a PN junction between the well region and a substrate ajoining the well region;
• (d) means for charging the well region to the voltage level of the first output conductor while the first depletion mode ground switch transistor is in its ON condition, and preventing escape of charge from the well region while the first depletion mode ground switch transistor is in its OFF condition by means of a parasitic diode associated with the second depletion mode protection transistor;
• and
• (e) means for charging the well region to a voltage equal to the control voltage signal minus a forward threshold voltage of the diode-connected enhancement mode transistor when the first reference voltage substantially exceeds the relatively low level thereof so the depletion mode ground switch transistor is in its OFF condition.