Patent ID: 8780048

Claim:
A membrane keyboard scan circuit used in a membrane keyboard having a key circuit, wherein the membrane keyboard scan circuit comprises: a row scan-port circuit comprising: a first select branch configured to be close when the membrane keyboard is a first type of the membrane keyboard, wherein the first select branch comprises: a first branch comprising a first switch and a first pull-up resistor connected to each other in series; and a third branch comprising a first input voltage control circuit and a third switch connected to each other in series; and a second select branch configured to be close when the membrane keyboard is a second type of the membrane keyboard, wherein the second select branch comprises: a second branch connected in parallel with the first branch between a first node and a second node, wherein the second branch comprises a second pull-up resistor having a different resistive value from that of the first pull-up resistor and a second switch connected to each other in series, and wherein the first node is connected to a power supply voltage; a fourth branch connected in parallel with the third branch between a third node and a fourth node, wherein the fourth branch comprises a second input voltage control circuit and a fourth switch connected to each other in series, the third node is a row output port of the row scan-port circuit, the second node and the fourth node are connected to a signal input port that is further connected to the key circuit, and the second input voltage control circuit has a different effective low threshold voltage level from that of the first input voltage control circuit; and a column scan-port circuit comprising: a fifth switch connected between the power supply voltage and a column output port of the column scan-port circuit; and a sixth switch having a first end connected to ground and a second end connected to the column output port of the column scan-port circuit; wherein the column scan-port circuit performs a scan output process repetitively to output a low voltage level in a first specific time period through the use of the fifth switch and the sixth switch and to output and maintain a high voltage level after the first specific time period to provide a row-scan timing signal to the key circuit of the membrane keyboard such that one of the first select branch and the second select branch generates a sensing signal when the key circuit is triggered.