Charge pump for use in non-volatile flash memory devices
Numerous embodiments of an improved charge pump design are disclosed for generating the high voltages necessary to perform erase and program operations in non-volatile flash memory devices. In these embodiments, each boost stage in the charge pump is modified to overcome a deficiency in prior art charge pumps whereby voltage actually would decrease in the final boost stage. These modifications include the addition of one or more of a clock doubling circuit, a local self-precharge circuit, a feed-forward precharge circuit, a feed-backward precharge circuit, and a hybrid circuit comprising NMOS and PMOS transistors and diodes.
1. A charge pump for receiving an input voltage and generating an output voltage, comprising:
a plurality of boost stages, each of the plurality of boost stages comprising:
an input node for the boost stage;
an output node for the boost stage;
a first capacitor comprising an input terminal for receiving a first clock signal and an output terminal coupled to the input node;
a second capacitor comprising an input terminal for receiving a second clock signal and an output terminal;
a first PMOS transistor comprising a first terminal coupled to the input node, a second terminal coupled to the output node, and a gate coupled to the output terminal of the second capacitor; and
a second PMOS transistor comprising a first terminal coupled to the output node, a second terminal coupled to the output terminal of the second capacitor, and a gate coupled to the input node;
wherein the input node for the boost stage is coupled to an output node of another boost stage in the plurality of boost stages or to a source providing the input voltage; and
wherein the output node for the boost stage is coupled to an input node of another boost stage in the plurality of boost stages or provides the output voltage.
2. The charge pump of claim 1 , wherein each of the plurality of boost stages further comprises:
a precharge gate comprising a first terminal coupled to a precharge voltage source, a gate coupled to the first terminal, and a second terminal coupled to the output node.
3. The charge pump of claim 1 , wherein each of the plurality of boost stages further comprises:
a third PMOS transistor comprising a first terminal coupled to the input node, a second terminal, and a gate coupled to the output node; and
a fourth PMOS transistor comprising a first terminal coupled to the second terminal of the third PMOS transistor, a second terminal coupled to the output node, and a gate coupled to the input node;
wherein a substrate of the first PMOS transistor, a substrate of the second PMOS transistor, a substrate of the third PMOS transistor, and a substrate of the fourth PMOS transistor are coupled to a common node.
4. The charge pump of claim 1 , further comprising a local precharge diode or transistor device.
5. The charge pump of claim 3 , wherein the second capacitor is a metal-oxide-metal (MOM) capacitor.
6. The charge pump of claim 3 , wherein the second capacitor is a metal-insulator-metal (MIM) capacitor.