# Patent

## Title
Voltage level shifter and method thereof

## Abstract

A voltage level shifter converts an input signal into an output signal. While the input signal is high to the output signal is high either. Moreover, while the input signal is low the output signal is low either.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a voltage level shifter, and in particular relates to a voltage level shifter avoiding current leakage.
2. Description of the Prior Art
Referring to FIG. 1, a schematic diagram of conventional voltage level shifter 100 is shown. Conventional voltage level shifter 100 includes: a inverting module 110, a latch circuit 140, inverting circuits 160 and 180 and an output circuit 195. Inverting module 110 includes NMOS transistors 111 and 112 and a PMOS transistor 113. NMOS transistor 111 has a drain for receiving an input signal Vin, a gate for receiving a voltage source VDD and a source coupled to ground voltage. NMOS transistor 112 has a drain coupled to node 121, a gate for receiving the input signal Vin and a source coupled to ground voltage. PMOS transistor 113 has a drain coupled to node 121, a gate for receiving the input signal Vin and a source for receiving the voltage source VDD.
Inverting circuit 160 includes NMOS transistors 161, 163, 164 and 165 and a PMOS transistor 162. NMOS transistor 161 has a drain coupled to the gate of NMOS transistor 163, a gate for receiving the input signal Vin and a source coupled to ground voltage. NMOS transistor 163 has a drain coupled to NMOS transistor 164, a gate coupled to NMOS transistor 161 and a source coupled to ground voltage. NMOS transistor 164 has a drain coupled to NMOS transistor 165, a gate for receiving the voltage source VDD and a source coupled to NMOS transistor 164. NMOS transistor 165 has a drain coupled to node N1, a gate for receiving a voltage source VBAT and a source coupled to NMOS transistor 164. PMOS transistor 162 has a drain coupled to NMOS transistor 161, a gate for receiving the input signal Vin and a source for receive the voltage source VDD. Voltage source VDD is generated from the voltage source VBAT by voltage dividing.
Inverting circuit 180 includes NMOS transistors 181, 183, 184 and 185 and a PMOS transistor 182. NMOS transistor 181 has a drain coupled to a gate of NMOS transistor 183, a gate coupled to node 121 and a source coupled to ground voltage. NMOS transistor 183 has a drain coupled to NMOS transistor 184, a gate coupled to NMOS transistor 181 and a source coupled to ground voltage. NMOS transistor 184 has a drain coupled to NMOS transistor 185, a gate coupled to the voltage source VDD and a source coupled to NMOS transistor 183. NMOS transistor 185 has a drain coupled to node N2, a gate coupled to the voltage source VBAT and a source coupled to NMOS transistor 184. PMOS transistor 182 has a drain coupled to NMOS transistor 181, a gate coupled to node 121 and a source for receiving the voltage source VDD.
Latch circuit 140 includes PMOS transistors 141 and 142. PMOS transistor 141 has a drain coupled to node N1, a gate coupled to node N2 and a source coupled to the voltage source VBAT. PMOS transistor 142 has a drain coupled to node N2, a gate coupled to node N1 and a source coupled to the voltage source VBAT. Output circuit 195 includes inverters 196 and 197. Inverter 196 is coupled between the voltage sources VBAT and VSS and has an input terminal coupled to node N1 and an output terminal coupled to inverter 197. Inverter 197 is also coupled between the voltage source VBAT and ground voltage and has an input terminal coupled to inverter 196 and an output terminal for outputting an output signal Vout.
Conventional voltage level shifter 100 can be used in logic circuits of a computer system. While the computer system does not provide voltage source VDD or voltage source VDD is low, inverters 196 and 197 have leakage current due to node N1 of voltage level shifter 100 is floating connected.
BRIEF SUMMARY OF THE INVENTION
A detailed description is given in the following embodiments with reference to the accompanying drawings.
An embodiment of a voltage level shifter is provided. The voltage level shifter for converting an input signal into an output signal includes: a first inverting module coupled between an input terminal and a first node for receiving an external signal and the input signal from the input terminal and providing a first signal at the first node; a second inverting module coupled between the first node and a second node for receiving the external signal and the input signal and providing the first signal at the first node; a first inverting protection circuit coupled between the first node and a third node for receiving the first signal and providing a second signal at the third node; a second inverting protection circuit coupled between the second node and a fourth node for receiving the input signal and providing a third signal at the fourth node; a latch circuit coupled between the third node and the fourth node for receiving the second signal, the third signal; and an output circuit receiving the second signal and outputting the output signal according to the second signal.
Another embodiment of a voltage shifting method is provided. The voltage shifting method for converting an input signal into an output signal includes: outputting a first signal according to the input signal and an external signal; generating a second signal according to the first signal; generating a third signal according to the input signal; generating the output signal according to the second signal and the third signal.



BRIEF DESCRIPTION OF the DRAWINGS
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 is a schematic diagram of conventional voltage level shifter; and
FIG. 2 is a schematic diagram of voltage level shifter according to an embodiment of the invention.



DETAILED DESCRIPTION OF THE INVENTION
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
Referring to FIG. 2, a schematic diagram of voltage level shifter 200 according to an embodiment of the invention is shown. Voltage level shifter 200 includes inverting modules 210 and 230, inverting protection circuits 260 and 280, a latch circuit 240 and an output circuit 295.
Inverting module 210 includes a resistor R2, an NMOS transistor T1 and PMOS transistors T2 and T3. Resistor R2 is coupled between PMOS transistor T3 and voltage source VBAT. NMOS transistor T1 has a drain coupled to node X1, a gate for receiving an input signal Vin and a source coupled to voltage VSS. PMOS transistor T2 has a drain coupled to node X1, a gate coupled to an external signal VEX and a source coupled to a drain of PMOS transistor T3. PMOS transistor T3 has a drain coupled to the source of PMOS transistor T2, a gate coupled to the input signal Vin and a source coupled to one terminal of resistor R2.
Inverting module 230 includes an inverter 235 and an NMOS transistor T4. Inverter 235 has an input terminal coupled to node X2 for receiving the input signal Vin, and an output terminal coupled to NMOS transistor T4. NMOS transistor T4 has a drain coupled to node X1, a gate coupled to the external signal VEX, and a source coupled to the output terminal of inverter 235. In addition, resistor R1 is coupled between node X2 and an voltage source VSS.
Inverting protection circuit 260 includes NMOS transistors T5, T6 and T7, a resistor R3 and a capacitor C1. NMOS transistor T5 has a drain coupled to NMOS transistor T6, a gate coupled to node X1, and a source coupled to voltage source VSS. NMOS transistor T6 has a drain coupled to NMOS transistor T7, a gate coupled to resistor R3 and capacitor C1, and a source coupled to NMOS transistor T5. NMOS transistor T7 has a drain coupled to node X3, a gate coupled to a voltage source VBAT and a source coupled to NMOS transistor T6. Resistor R3 is coupled between the gate of NMOS transistor T6 and the voltage source VBAT. Capacitor C1 is coupled between resistor R3 and voltage source VSS.
Inverting protection circuit 280 includes NMOS transistors T8, T9 and T10, resistor R4 and capacitor C2. NMOS transistor T8 has a drain coupled to NMOS transistor T6, a gate coupled to node X2 and a source coupled to voltage source VSS. NMOS transistor T9 has a drain coupled to NMOS transistor T10, a gate coupled to resistor R4 and capacitor C2, and a source coupled to NMOS transistor T8. NMOS transistor T10 has a drain coupled to node X4, a gate coupled to voltage source VBAT and a source coupled to NMOS transistor T9. Resistor R4 is coupled between the gate of NMOS transistor T9 and voltage source VBAT. Capacitor C2 is coupled between resistor R4 and voltage VSS.
Latch circuit 240 includes PMOS transistors T11 and T12. PMOS transistor T11 has a drain coupled to node X3, a gate coupled to node X4 and a source coupled to voltage source VBAT. PMOS transistor T12 has a drain coupled to node X4, a gate coupled to node X3 and a source coupled to voltage source VBAT. Output circuit 295 includes two inverters 296 and 297. Inverter 296 coupled between voltage source VBAT and voltage source VSS and having an input terminal coupled to node X3 and an output terminal coupled to inverter 297. Inverter 297 coupled between voltage source VBAT and voltage source VSS and having an input terminal coupled to inverter 296 and an output terminal to an output signal Vout.
In the present invention, assume the ranges of input signal Vin and external signal VEX are 0V ̃0.9V (or 0V ̃1.2V), voltage source VBAT is substantially equal to 3.3V, and voltage source VSS is a ground voltage. As a result, output signal Vout is ranged from 0V to 3.3V. According to the operations of voltage level shifter 200 in the present invention, output signal Vout is at low voltage level (i.e. 0V) while input signal Vin is at low voltage level (i.e. 0V); moreover, output signal Vout is at high voltage level (i.e. 3.3V) while input signal Vin is at high voltage level (i.e. 0.9V). Four operating embodiments will be described in more detail set below.
Referring to FIG. 2, for the first embodiment of the present invention, assume that external signal VEX and input signal Vin are both at high voltage level (i.e. 0.9V). Therefore, node X2 is at high voltage level, NMOS transistor T8 turns on, NMOS transistor T4 turns on, NMOS transistor T1 turns on and node X1 is at low voltage level. Then, NMOS transistor T5 turns off. In addition, voltage source VBAT is at high voltage level (i.e. 3.3V) and biases the gates of NMOS transistors T6, T7, T9 and T10; as a result, NMOS transistors T6, T7, T9 and T10 are turned on. Consequentially, node X4 is at low voltage level, PMOS transistor T11 turns on and node X3 is at high voltage level (VBAT). Output circuit 295 receives an input signal with a high voltage level from node X3 and then outputs an output signal Vout with a high voltage level (i.e. 3.3V) accordingly.
Referring to FIG. 2, for the second embodiment of the present invention, assume that external signal VEX is high voltage level (i.e. 0.9V) and input signal Vin is at low voltage level (i.e. 0V). Therefore, node X2 is at low voltage level, NMOS transistor T8 turns off, NMOS transistor T4 turns on and node X1 is at high voltage level. Then, NMOS transistor T5 turns on. Voltage source VBAT is at high voltage level (i.e. 3.3V) and biases the gates of NMOS transistors T6, T7, T9 and T10; as a result, NMOS transistors T6, T7, T9 and T10 are turned on. Consequentially, node X3 is at low voltage level, PMOS transistor T12 turns on and node X4 is at high voltage level (i.e. VBAT). Output circuit 295 receives an input signal with a low voltage level from node X3 and then outputs an output signal Vout with a low voltage level (i.e. 0V) accordingly.
Referring to FIG. 2, for the third embodiment of the present invention, assume that external signal VEX is at low voltage level (i.e. 0V) and input signal Vin is at high voltage level (i.e. 0.9V). Therefore, node X2 is at high voltage level, NMOS transistor T8 turns on, NMOS transistor T4 turns off, NMOS transistor T1 turns on and node X1 is at low voltage level. Then, NMOS transistor T5 turns off. Voltage source VBAT is at high voltage level (i.e. 3.3V) and biases to gates of NMOS transistors T6, T7, T9 and T10; as a result, NMOS transistors T6, T7, T9 and T10 are turned on. Node X4 is at low voltage level. PMOS transistor T11 is turned on. Consequentially, node X3 is at high voltage level (i.e. VBAT). Output circuit 295 receives an input signal with high voltage level signal from node X3 and then outputs an output signal Vout with high voltage level (i.e. 3.3V) accordingly.
Referring to FIG. 2, for the fourth embodiment of the present invention, assume that external signal VEX and input signal Vin are both at low voltage level (i.e. 0V). Therefore, node X2 is at low voltage level, NMOS transistor T8 turns off, NMOS transistor T4 turns on, NMOS transistors T2 and T3 also turn on and node X1 is at high voltage level. Then, NMOS transistor T5 turns on. Voltage source VBAT is at high voltage level (i.e. 3.3V) and biases to gates of NMOS transistors T6, T7, T9 and T10; as a result, NMOS transistors T6, T7, T9 and T10 are turned on. Consequentially, node X3 is at low voltage level, PMOS transistor T12 turns on, node X4 is at high voltage level (i.e. VBAT). Output circuit 295 receives an input signal with low voltage level signal from node X3 and then outputs an output signal Vout with a low voltage level (i.e. 0V) accordingly.
Table 1 shows the four embodiments according to the above descriptions. As shown in Table 1, regardless of the voltage level of external signal VEX, the voltage level shifter 200 can normally output the output signal Vout according to the input signal Vin. In other words, the voltage level of output signal Vout would follow the voltage level of input signal Vin. Thus, while an input signal Vin with low voltage level is inputted to voltage level shifter 200, an output signal Vout with low voltage level is consequentially outputted. While an input signal Vin with high voltage level is inputted into voltage level shifter 200, an output signal Vout with high voltage level is consequentially outputted. Comparing to the conventional voltage level shifter 100, while voltage source VDD is at low voltage level, current leakage of inverters 196 and 197 would occur due to a floating node N1 of voltage level shifter 100.













TABLE 1









Intput signal (Vin)
High
Low
High
Low



External signal (VEX)
High
High
Low
Low



Output signal (Vout)
VBAT
Vss
VBAT
Vss



Node X1
Vss
VBAT
Vss
VBAT



Node X2
Vin
Vin
Vin
Vin



Node X3
VBAT
Vss
VBAT
Vss



Node X4
Vss
VBAT
Vss
VBAT










While the invention has been described by way of example and in terms of preferred embodiments, it is to be understood that the invention is not limited to thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

## Claims

1. A voltage level shifter for converting an input signal into an output signal, comprising
a first inverting module coupled between an input terminal and a first node for receiving an external signal and the input signal from the input terminal and providing a first signal at the first node;
a second inverting module coupled between the first node and a second node for receiving the external signal and the input signal and providing the first signal at the first node;
a first inverting protection circuit coupled between the first node and a third node for receiving the first signal and providing a second signal at the third node;
a second inverting protection circuit coupled between the second node and a fourth node for receiving the input signal and providing a third signal at the fourth node;
a latch circuit coupled between the third node and the fourth node for receiving the second signal and the third signal; and
an output circuit receiving the second signal and outputting the output signal according to the second signal.

2. The voltage level shifter as claimed in claim 1, wherein when the input signal and the external voltage are both at high voltage level, the first signal and the third signal are at low voltage level, the second signal is at high voltage level and the output signal is at high voltage level.

3. The voltage level shifter as claimed in claim 1, wherein when the input signal and the external voltage are both at low voltage level, the first signal and the third signal are at high voltage level, the second signal is at low voltage level and the output signal is at low voltage level.

4. The voltage level shifter as claimed in claim 1, wherein when the input signal is at low voltage level and the external voltage is at high voltage level, the first signal and the third signal are at high voltage level, the second signal is at low voltage level and the output signal is at low voltage level.

5. The voltage level shifter as claimed in claim 1, wherein when the input signal is at high voltage level and the external voltage is at low voltage level, the first signal and the third signal are at low voltage level, the second signal is at high voltage level and the output signal is at high voltage level.

6. The voltage level shifter as claimed in claim 1 wherein the output circuit comprises a first inverter coupled to a second inverter in series, for sequentially inverting the second signal and outputting the output signal.

7. The voltage level shifter as claimed in claim 1 wherein the first inverting module comprises:
a first transistor, a second transistor and a third transistor cascaded between a voltage source and a ground voltage; and
wherein the input signal is respectively applied to gates of the first and the third transistors, the external signal is applied to gate of the second transistor, and the first signal is provided from a junction node of the first transistor and the second transistor.

8. The voltage level shifter as claimed in claim 1 wherein the second inverting module comprises:
a first inverter receiving the input signal; and
a first transistor coupled between the first inverter and the first node, the first transistor has a gate for receiving the external signal and provides the first signal at the first node.

9. The voltage level shifter as claimed in claim 1 wherein the first inverting protection circuit comprises:
a first transistor, a second transistor and a third transistor cascaded between the third node and a ground voltage;
wherein the first signal from the first node is applied to gate of the first transistor, a voltage source is respectively applied to gates of the second and the third transistors, and the second signal is provided at drain of the third transistor.

10. The voltage level shifter as claimed in claim 1 wherein the second inverting protection circuit comprises:
an first transistor, a second transistor and a third transistor cascaded between the fourth node and a ground voltage;
wherein the input signal is applied to gate of the first transistor via the second node, a voltage source is respectively applied to gates of the second and the third transistors, and the third signal is provided at drain of the third transistor.

11. The voltage level shifter as claimed in claim 1 wherein the latch circuit comprises:
an first transistor having a gate for receiving the third signal from the fourth node, a source coupled to a voltage source and a drain coupled to the first inverting protection circuit via the third node; and
a second transistor having a gate for receiving the second signal form the third node, a source coupled to the voltage source and a drain coupled to the second inverting protection circuit via the fourth node.

12. The voltage level shifter as claimed in claim 1 wherein the external signal and the input signal are in the range from 0V to 1.2V.

13. The voltage level shifter as claimed in claim 1 wherein the output signal is in the range from 0V to 3.3V.