MOFSET mismatch characterization circuit
View Patent ↗A semiconductor device comprises a plurality of transistor mismatch circuits formed on a semiconductor wafer; and a characterization circuit formed on the semiconductor wafer. The characterization circuit is coupled to receive input provided by the absolute value circuits simultaneously which themselves receive inputs from the mismatch circuits simultaneously and is configured to output a standard deviation of mismatch between transistors in the mismatch circuits.
1. A semiconductor device comprising:
a summing amplifier;
a plurality of transistor mismatch circuits, wherein the transistor mismatch circuits output a value indicative of mismatch between transistors in a respective one of the transistor mismatch circuits; and
first output voltages Vo 1 and second output voltages Vo 2 from each of the transistor mismatch circuits coupled simultaneously to an input of the summing amplifier, wherein the summing amplifier provides a value indicating a standard deviation of the mismatch between the transistors in the plurality of mismatch circuits simultaneously with the first and second output voltages of the plurality of transistor mismatch circuits being applied to the summing amplifier.
2. The semiconductor device of claim 1 further comprising:
the summing amplifier includes a first operational amplifier coupled in parallel to a first resistor; and
a plurality of second resistors coupled in series between respective transistor mismatch circuits and the summing amplifier.
3. The semiconductor device of claim 2 further comprising:
the first resistor has a value of R ohms; and
the second resistors have a value equal to the value of the first resistor times the number of transistor mismatch circuits times the square root of 2 divided by pi (√(2/π)).
4. The semiconductor device of claim 1 , wherein the transistor mismatch circuits comprise:
a first inverter circuit including a first PMOS transistor and a first NMOS transistor, a drain electrode of the first PMOS transistor coupled to a drain electrode of the first NMOS transistor;
a second inverter circuit including a second PMOS transistor and a second NMOS transistor, a drain electrode of the second PMOS transistor coupled to a drain electrode of the second NMOS transistor;
one of the first output voltages Vo 1 coupled to gate electrodes of the first and second PMOS and NMOS transistors, and between the drain electrode of the first PMOS transistor and the drain electrode of the first NMOS transistor to self-bias the first inverter circuit; and
one of the second output voltages Vo 2 coupled between the drain electrode of the second PMOS transistor and the drain electrode of the second NMOS transistor.
5. The semiconductor device of claim 1 further comprising:
a plurality of absolute value circuits coupled between respective transistor mismatch circuits and the summing amplifier.
6. The semiconductor device of claim 5 , wherein the absolute value circuits include
a comparator that has
a first input coupled to a respective first output voltage Vo 1 of one of the transistor mismatch circuits,
a second input coupled to a respective second output voltage Vo 2 from one of the transistor mismatch circuits, and
an output that is used to select inputs to a unity gain buffer; and
a unity gain buffer configured to receive a first input and a second input, and to provide the unity gain buffer output indicating the absolute value of the difference between the second output voltage and the first output voltage of the respective transistor mismatch circuit,
the first input of the unity gain buffer is coupled to a first set of switches that operate based on the output of the comparator to provide the first output voltage to the first input of the unity gain buffer when the first output voltage is less than the second output voltage, and to provide the second output voltage to the first input of the unity gain buffer when the second output voltage is less than the first output voltage, and
the second input of the unity gain buffer is coupled to a second set of switches that operate based on the output of the comparator to provide the first output voltage to the second input of the unity gain buffer when the first output voltage is greater than the second output voltage, and to provide the second output voltage to the second input of the unity gain buffer when the second output voltage is greater than the first output voltage.
7. The semiconductor device of claim 5 wherein the absolute value circuits further include:
a second resistor coupled between the first output voltage Vo 1 and a first input of a second operational amplifier;
a third resistor coupled between the second output voltage Vo 2 and a second input of the second operational amplifier;
a fourth resistor coupled between the first input of the second operational amplifier and an output of the second operational amplifier;
a fifth resistor coupled between the second input of the second operational amplifier and ground;
a sixth resistor coupled between the output of the second operational amplifier and a first input of a third operational amplifier;
a seventh resistor coupled between the output of the second operational amplifier and a first input of a fourth operational amplifier;
an eighth resistor coupled between the first input of the fourth operational amplifier and a diode;
a ninth resistor including one terminal coupled between the eighth resistor and diode, another terminal coupled to one input of the third operational amplifier;
a first diode coupled between the output of the third operational amplifier and the eighth resistor;
a second diode coupled between the first input of the third operational amplifier and the output of the third operational amplifier;
a second input of the third operational amplifier is coupled to ground;
a tenth resistor coupled between the first input of the fourth operational amplifier and the output of the fourth operational amplifier; and
a second input of the fourth operational amplifier is coupled to ground.
8. The semiconductor device of claim 5 wherein the summing amplifier 206 includes a first operational amplifier with a resistor coupled between an output of the first operational amplifier and a first input of the first operational amplifier and with a second input of the first operational amplifier coupled to ground.
9. A method comprising:
forming a plurality of transistor mismatch circuits on a semiconductor wafer;
forming a summing amplifier on the wafer, wherein the summing amplifier is electrically coupled to receive first and second output voltages from each of the plurality of mismatch circuits simultaneously;
simultaneously applying supply voltages Vss and Vdd to the plurality of transistor mismatch circuits during probe testing; and
measuring an output of the summing amplifier while the supply voltages are simultaneously applied to the plurality of the transistor mismatch circuits and the first and second output voltages from each of the plurality of mismatch circuits are simultaneously applied to the summing amplifier on the wafer, wherein the output of the summing amplifier indicates a standard deviation of the mismatch between the transistors in the plurality of mismatch circuits.
10. The method of claim 9 further comprising:
forming a plurality of absolute value circuits coupled between the transistor mismatch circuits and the summing amplifier.
11. The method of claim 9 wherein the output of the summing amplifier represents a characteristic of mismatch between similar types of transistors on the semiconductor wafer.
12. The method of claim 11 wherein the mismatch circuits include a first self-biasing inverter circuit having a first PMOS transistor coupled to a first NMOS transistor, and a second inverter circuit having a second PMOS transistor couple to a second NMOS transistor, and the characteristic of mismatch is standard deviation of mismatch between similar types of the transistors.
13. The method of claim 9 wherein the mismatch circuits are formed in at least one of: a scribe street on the wafer, and in an integrated circuit die on the wafer.
14. A semiconductor device comprising:
a plurality of transistor mismatch circuits formed on a semiconductor wafer; and
a characterization circuit formed on the semiconductor wafer, the characterization circuit is coupled to receive first and second output voltages provided by each of the mismatch circuits simultaneously and is configured to output a standard deviation of mismatch between transistors in the plurality of mismatch circuits simultaneously with receiving the first and second output voltages provided by each of the mismatch circuits simultaneously.
15. The semiconductor device of claim 14 further comprising:
a plurality of absolute value circuits coupled between respective transistor mismatch circuits and the characterization circuit, wherein the absolute value circuits are configured to receive input from the transistor mismatch circuits and to output an absolute value of the input.
16. The semiconductor device of claim 14 , the mismatch circuits comprising:
a first PMOS transistor and a first NMOS transistor configured as a first stage inverter circuit; and
a second PMOS transistor and a second NMOS transistor configured as a second stage inverter circuit that is coupled to the first inverter circuit.
17. The semiconductor device of claim 15 further comprising:
a plurality of resistors, wherein each of the resistors is coupled between the output of a respective one of the absolute value circuits and the characterization circuit, and the value of the resistors is proportional to the number of mismatch circuits.
18. The semiconductor device of claim 17 wherein the characterization circuit is a summing amplifier that includes a first operational amplifier with a resistor coupled between an output of the first operational amplifier and a first input and a second input coupled to ground.
19. The semiconductor device of claim 14 wherein the transistor mismatch circuits comprise:
a first inverter circuit including a first PMOS transistor and a first NMOS transistor, a drain electrode of the first PMOS transistor coupled to a drain electrode of the first NMOS transistor;
a second inverter circuit including a second PMOS transistor and a second NMOS transistor, a drain electrode of the second PMOS transistor coupled to a drain electrode of the second NMOS transistor;
one of the first output voltages coupled to gate electrodes of the first and second PMOS and NMOS transistors, and between the drain electrode of the first PMOS transistor 208 and the drain electrode of the first NMOS transistor to self-bias the first inverter circuit; and
one of the second output voltages coupled between the drain electrode of the second PMOS transistor and the drain electrode of the second NMOS transistor.
20. The semiconductor device of claim 14 wherein the mismatch circuits are formed in at least one of: a scribe street on the wafer, and in an integrated circuit die on the wafer.