Author: claimsbot

1. A paper dispenser comprising:
a housing having an inner chamber adapted to support a roll of paper and having a dispensing aperture;
a motor adapted to dispense paper from the roll of paper through the dispensing aperture; and
a proximity detection circuit for detecting the presence of a moving hand in the vicinity of said dispensing aperture, said circuit comprising:
an antenna with which is associated a fixed time constant determined by a predetermined capacitance and a predetermined resistance, as well as a variable time constant that is longer than the fixed time constant by an amount determined by an external capacitive load, said variable time constant being on the order of twice said fixed time constant when the external capacitive load is a hand of a person in proximity to the antenna;
an oscillator circuit for charging the antenna with an oscillating signal with a periodicity greater than said fixed time constant;
an operational amplifier being operated as a unity gain follower and receiving an antenna signal from the antenna, the antenna signal being representative of an external capacitive load on the antenna and having a periodic exponential waveform that has a longer time constant and a lower amplitude when said external capacitive load is in proximity to said antenna, the waveform of the antenna signal being thus representative of changes in the external capacitive load on the antenna;
a detector circuit electrically coupled to the operational amplifier for detecting changes in a low frequency component of the antenna signal and for generating a detection signal in response thereto; and
a comparator responsive to the detection signal for generating an output signal to said motor when the detection signal is representative of a waving hand in proximity to the antenna.
2. The paper dispenser of claim 1, the proximity detection circuit further comprising at least one static protection circuit having at least one first diode adapted to conduct away from ground and at least one second diode adapted to conduct toward a supply voltage.
3. The paper dispenser of claim 1, the proximity detection circuit further comprising a voltage peak detector.
4. The paper dispenser of claim 1, the proximity detection circuit further comprising a low-pass filter electrically coupled between the detector circuit and the comparator for passing said low frequency signal component and rejecting a higher frequency noise component.
5. The paper dispenser of claim 4, the proximity detection circuit further comprising a gain and offset amplifier electrically coupled between the low-pass filter and the comparator, for amplifying said low frequency signal component.
6. The paper dispenser of claim 1, wherein the comparator is adapted to actuate the motor when the detection signal has a predetermined voltage level as compared to a reference voltage.
7. A paper dispenser comprising:
a housing having an inner chamber adapted to support a roll of paper and having a dispensing aperture;
a motor adapted to dispense paper from the roll of paper through the dispensing aperture; and
a proximity detection circuit for detecting the presence of a moving hand, said circuit comprising:
an antenna with which is associated a fixed time constant determined by a predetermined capacitance and a predetermined resistance, as well as a variable time constant that is longer than the fixed time constant by an amount determined by an external capacitive load, said variable time constant being on the order of twice said fixed time constant when the external capacitive load is a hand of a person in proximity to the antenna;
means for charging the antenna with an oscillating signal with a periodicity greater than said fixed time constant;
means for buffering an antenna signal from the antenna, the antenna signal being representative of an external capacitive load on the antenna and having a periodic exponential waveform that has a longer time constant and a lower amplitude when said external capacitive load is in proximity to said antenna, the waveform of the buffered antenna signal being thus representative of changes in the external capacitive load on the antenna;
means for detecting changes in a low frequency component of the buffered antenna signal and for generating a detection signal in response thereto; and
means for generating an output signal to said motor when the detection signal is representative of a waving hand in proximity to the antenna.
8. The paper dispenser of claim 7, the proximity detection circuit further comprising at least one static protection circuit having at least one first diode adapted to conduct away from ground and at least one second diode adapted to conduct toward a supply voltage.
9. The paper dispenser of claim 7, the proximity detection circuit further comprising means for filtering alternating current interference frequencies from the detection signal.
10. The paper dispenser of claim 7, the proximity detection circuit further comprising means for amplifying the detection signal.
11. The paper dispenser of claim 7, the proximity detection circuit further comprising means for detecting a voltage peak in the buffered antenna signal.
12. The paper dispenser of claim 7, wherein the output signal actuates the motor when the detection signal has a predetermined voltage level as compared to a reference voltage.
13. A paper dispenser comprising:
means for supporting a roll of paper within a housing;
means for dispensing paper from the roll of paper;
a proximity detector circuit comprising:
an antenna with which is associated a fixed time constant determined by a predetermined capacitance and a predetermined resistance, as well as a variable time constant that is longer than the fixed time constant by an amount determined by an external capacitive load, said variable time constant being on the order of twice said fixed time constant when the external capacitive load is a hand of a person in proximity to the antenna;
an oscillator circuit for charging the antenna with an oscillating signal with a periodicity greater than said fixed time constant;
an operational amplifier being operated as a unity gain follower and receiving an antenna signal from the antenna;
a detector circuit electrically coupled to the operational amplifier for detecting changes in a low frequency component of the antenna signal, the antenna signal being representative of an external capacitive load on the antenna and having a periodic exponential waveform that has a longer time constant and a lower amplitude when said external capacitive load is in proximity to said antenna, and for generating a detection signal in response thereto; and

a comparator responsive to the detection signal for generating an output signal to said dispensing means when the detection signal is representative of a waving hand in proximity to the antenna.
14. The paper dispenser of claim 13, the proximity detection circuit further comprising at least one static protection circuit having at least one first diode adapted to conduct away from ground and at least one second diode adapted to conduct toward a supply voltage.
15. The paper dispenser of claim 13, wherein the output signal actuates the motor when the detection signal has a predetermined voltage level as compared to a reference voltage.
16. A paper dispenser comprising:
a housing having an inner chamber adapted to support a roll of paper and having a dispensing aperture;
a motor disposed within the housing and adapted to dispense paper from the roll of paper through the dispensing aperture; and
a proximity detection circuit disposed within the housing, the proximity detection circuit comprising:
an antenna;
an asymmetric oscillator circuit electrically coupled to the antenna, the asymmetric oscillator circuit having an on-period and an off-period, wherein the asymmetric oscillator circuit is adapted to send an approximately uniform charge to the antenna during the on-period;
an antenna impedance buffer electrically coupled to the antenna, the antenna impedance buffer including an operational amplifier adapted to operate as a unity gain follower;
a voltage peak detector electrically coupled to an output of the antenna impedance buffer, the voltage peak detector comprising a diode, a current-limiting resistor, a peak storage capacitor, and a bleed off resistor, the diode and the peak storage capacitor being adapted to capture positive peaks of exponential waveforms from the antenna impedance buffer, the current limiting resistor being adapted to limit current flow from the antenna impedance buffer, and the bleed-off resistor being adapted to provide a discharge pathway for the peak storage capacitor,
a gain and voltage offset amplifier electrically coupled to an output of the voltage peak detector,

an output comparator adapted to receive an input signal from the gain and voltage offset amplifier and a reference voltage, the output comparator being further adapted to actuate the motor when the input signal has a predetermined voltage level as compared to the reference voltage, and
an auto-compensation capacitor electrically coupled between the gain and voltage offset amplifier and the output comparator, the auto-compensation capacitor being adapted to filter out changes in DC voltage levels in the signal while allowing passage of transient portions of the signal representative of a waving hand in proximity to the antenna.
17. The paper dispenser of claim 16, the proximity detection circuit further comprising at least one static protection circuit having at least one second diode adapted to conduct away from ground and at least one third diode adapted to conduct toward a supply voltage.
18. The paper dispenser of claim 16, wherein the current limiting resistor is adapted to prevent oscillation at the antenna impedance buffer.
19. The paper dispenser of claim 16, the proximity detection circuit further comprising a low-pass filter electrically coupled between the voltage peak detector and the output comparator, the low-pass filter being adapted to filter out about 50 or about 60 Hz alternating current interference frequencies.
20. A method of dispensing paper comprising:
supporting a roll of paper within a housing, the housing including a dispensing aperture and having a motor affixed thereto;
affixing an antenna to the housing;
charging the antenna with an oscillating signal to thereby produce a periodic antenna signal, the antenna having an associated fixed time constant determined by a predetermined capacitance and a predetermined resistance, as well as a variable time constant that is longer than the fixed time constant by an amount determined by an external capacitive load, said variable time constant being on the order of twice said fixed time constant when the external capacitive load is a hand of a person in proximity to the antenna, said oscillating signal having a periodicity greater than said fixed time constant,
detecting low frequency changes in the antenna signal representative of changes in said external capacitive load on the antenna caused by a moving hand in proximity to the antenna;
generating a low frequency detection signal component in response to said low frequency changes in the antenna signal;
selectively amplifying said low frequency detection signal component and rejecting a higher frequency noise component to thereby produce an amplified and filtered detection signal component;
compensating for slow environmental changes in the amplified and filtered detection signal component to thereby provide a compensated detection signal with increased sensitivity to transient signals representative of a waving hand in proximity to the antenna; and
actuating the motor in response to the compensated detection signal, wherein the motor is adapted to dispense paper from the roll of paper through the dispensing aperture upon actuation.
21. The method of claim 20, wherein actuating the motor includes comparing the detection signal to a reference voltage.
22. The method of claim 20, wherein charging the antenna with the oscillating signal includes charging the antenna with an oscillating asymmetric signal.
23. The method of claim 20, wherein detecting changes in the antenna signal includes detecting a peak voltage.
24. The method of claim 20 further comprising providing protection from static utilizing at least one static protection circuit having at least one first diode adapted to conduct away from ground and at least one second diode adapted to conduct toward a supply voltages.
25. The method of claim 20 further comprising providing a current limiting resistor to prevent oscillation in the low frequency detection signal.
26. The method of claim 20 further comprising filtering out alternating current interference frequencies from the antenna signal.
27. The method of claim 20 further comprising wherein compensating for slow environmental changes includes filtering out changes in DC voltage levels from the detection signal component while passing transient portions thereof.
28. A method of dispensing paper comprising:
supporting a roll of paper within a housing, the housing including a dispensing aperture and having a motor affixedd thereto;
producing an oscillating asymmetric signal having an on period and an off period;
charging an antenna with the oscillating asymmetric signal, the antenna being affixed to the housing, wherein the oscillating asymmetric signal is adapted to provide an approximately uniform amount of charge to the antenna during the on period;
discharging the antenna to a fixed voltage for every oscillation period;
buffering any impedance mismatch between the antenna and a peak detector utilizing an operational amplifier adapted to operate as a unity gain follower;
detecting a peak voltage in the antenna discharge with the peak detector;
offsetting and amplifying the detected peak voltage from the peak detector;
filtering out changes in DC voltage levels of the offset and amplified peak voltage while allowing passage of transient portions thereof; and
actuating the motor upon detection in said transient portions of a signal which is within predetermined duration, amplitude, and rate of change criteria, wherein the motor is adapted to dispense paper from the roll of paper through the dispensing aperture upon actuation.
29. The method of claim 28, wherein detecting the peak voltage includes providing the peak detector with a diode and a peak storage capacitor, the diode and peak storage capacitor being adapted to capture peaks of exponential waveforms output from the operational amplifier.
30. The method of claim 28 further comprising providing protection from static utilizing at least one static protection circuit having at least one first diode adapted to conduct away from ground and at least one second diode adapted to conduct toward the supply voltage.
31. The method of claim 28 further comprising preventing oscillation by including a current limiting resistor at the output terminal of the operational amplifier.
32. The method of claim 28, wherein after detecting the peak voltage the method further comprises filtering out about 50 Hz and about 60 Hz alternating current interference frequencies through a low-pass filter.
33. The method of claim 28, wherein actuating the motor includes comparing the signal to a reference voltage to determine if the signal has a predetermined voltage level as compared to the reference voltage.

The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.

1. A method for growing a nitride-based semiconductor with high quality, the method comprising:
forming a first mask layer on a substrate and forming a second mask layer on the first mask layer;
performing dry etching on the first mask layer and the second mask layer to form an opening in which a part of the substrate is exposed;
performing selective wet etching on the first mask layer in the opening to form a recess in which a part of the substrate is exposed;
depositing a third mask layer in the recess; and
growing a nitride-based semiconductor from the exposed part of the substrate on sides of the third mask layer and expanding the growth via the opening.
2. The method of claim 1, further comprising:
performing wet etching on the first mask layer, the second mask layer and the third mask layer to form a void after the nitride-based semiconductor expanded via the opening is re-grown and is merged with another nitride-based semiconductor re-grown from an adjacent opening to cover a upper side of the second mask layer; and
removing the nitride-based semiconductor grown in the opening from the void.
3. The method of claim 1, further comprising:
forming a pattern on the second mask layer before the performing the dry etching.
4. The method of claim 1, each of the first mask layer, the second mask layer and the third mask layer comprises one of SiO2, SiN, Si3N4, ZnS, Ta2O5, TiO2, ZrO2, Y2O3, STO (SrTiO3), BST ((Ba,Sr)TiO3), PZT (PbZrxTiyOz) and silicon oxynitride (SiON)
5. The method of claim 1, wherein an etching rate of the first mask layer is larger than an etching rate of the second mask layer.
6. The method of claim 1, wherein the third mask layer is made of the same material as or a different material from a material of the first mask layer or a material of the second mask layer.
7. The method of claim 1, wherein the performing the wet etching comprises:
performing the wet etching at a temperature between a room temperature and 350\xb0 C. using one of:
hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), phosphoric acid (H3PO4), oxalic acid, buffered oxide etchant (BOE), sodium hydroxide (NaOH), potassium hydroxide (KOH), hydrogen peroxide (H2O2), acetone, tetramethyl armmonium hydroxide (TMAH), ethylenediamine, pyrocatechol, hydrazine chelating amines, 1,2-diaminoethane, N,N-dimethylacetamide and water, or a mixed solution prepared as a combination thereof.
8. The method of claim 1, wherein the performing the dry etching comprises using at least one gas selected from the group consisting of Cl2, HBr, HCl, SF6, CF4, CHF3, NF3, O2 and chlorofluorocarbons (CFCs).
9. The method of claim 1, wherein the performing the dry etching further comprises using at least one of N2, Ar and He inert gases.
10. The method of claim 1, the substrate is made of a material selected from the group consisting of sapphire, Si, glass, quartz, GaN, GaAs, SiC, ZnO and MgO.
11. The method of claim 1, wherein the nitride-based semiconductor is expressed in the following formula: AlxGayIn1\u2212x\u2212yN (0\u2266x\u22661, 0\u2266y\u22661, 0\u2266x+y\u22661).

We claim:

1. A method for optimizing communication on a network comprising a master device and a slave device, each device utilizing TCP and IP protocols, the method comprising the steps of:
transmitting a request message from the master device, the request message having a first part;
transmitting a response message from the slave device, the response message being responsive to the first part of the request message; and,
limiting the request message and the response message to a length that is less than both a TCP transaction length and a maximum transmission unit.
2. The method of claim 1 wherein MODBUS is utilized as an application layer protocol.
3. The method of claim 2 further including:
designating a set of predetermined response messages comprising at least one predetermined response message, each predetermined response message being distinguishable by the first part of the request message; and,
selecting a predetermined response message in response to the first part of the request message wherein the predetermined response message is rapidly determined from the content of the first part of the request message for quickly responding to the request message.
4. The method of claim 3 wherein the set of predetermined response messages comprises a response message to an address resolution protocol request message.
5. The method of claim 3 wherein the set of predetermined response messages comprises a response message to an Internet control management protocol request message.
6. The method of claim 3 wherein the set of predetermined response messages comprises a response message to a TCP connection request message.
7. The method of claim 3 wherein the set of predetermined response messages comprises a response message to a TCP disconnect request message.
8. The method of claim 3 wherein the set of predetermined response messages comprises a response message to a MODBUS request message as a TCP data frame.
9. The method of claim 1 wherein the message is received exclusively on TCP port number 502.
10. The method of claim 9 further including ignoring any message that is not transmitted via a TCP port number 502.
11. A network communication system comprising:
a master device for initiating a request message;
a slave device being exclusively responsive to the request message of the master device; and,
an optimal protocol utilized to communicate the request message and the response message between the master and the slave devices, the optimal protocol comprising:
an IP protocol;
a TCP protocol; and,
an application layer protocol wherein the building and parsing of the response message is responsive to a first part of the request message.
12. The network communication system of claim 11 wherein the application layer protocol is MODBUS.
13. The network communication system of claim 11 wherein the response message is responsive to the content of the first part of the request message 14. The network communication system of claim 11 wherein the master device exclusively initiates the request message.
14. The network communication system of claim 11 wherein the master device exclusively initiates the request message.
15. The network communication system of claim 11 further comprising a set of predetermined response messages including at least one predetermined response message, each predetermined response message being distinguishable by the first part of the request message wherein the predetermined response message is determined from the content of the first part of the request message and rapidly selected for quickly responding to the request message.
16. The network communication system of claim 15 wherein the set of predetermined response messages comprises a response message to an address resolution protocol request message.
17. The network communication system of claim 15 wherein the set of predetermined response messages comprises a response message to an Internet control management protocol request message.
18. The network communication system of claim 15 wherein the set of predetermined response messages comprises a response message to a TCP connection request message.
19. The network communication system of claim 15 wherein the set of predetermined response messages comprises a response message to a TCP disconnect request message.
20. The network communication system of claim 15 wherein the set of predetermined response messages comprises a response message to a MODBUS request message as a TCP data frame.
21. The network communication system of claim 11 wherein each device limits its message to a length that is less than both a TCP transaction length and a maximum transmission unit.
22. The network communication system of claim 11 wherein the optimal protocol exclusively utilizes a TCP port number 502.
23. The network communication system of claim 22 wherein any message not transmitted via the TCP port number 502 is ignored.
24. A high performance Ethernet module comprising:
an Ethernet controller operably coupled to a network connection;
a control processing unit operably coupled to the Ethernet controller; and,
an optimal communication stack that executes on the control processing unit, the optimal communication stack being capable of simultaneously processing a TCP protocol, an IP protocol and an application layer protocol, the simultaneous processing further including building and parsing a communication message dependent upon a predetermined index of the message.
25. The Ethernet module of claim 24 wherein the application layer protocol is MODBUS.
26. The Ethernet module of claim 25 wherein the communication message is limited to a length that is less than both a TCP transaction length and a maximum transmission unit.
27. The Ethernet module of claim 24 wherein the optimal communication stack is configured to quickly provide a response message responsive to a request message.
28. The Ethernet module of claim 27 wherein the communication message further comprises the request message having a first portion and the response message being responsive to the first portion of the request message wherein the response message is determined from the content of the first portion of the request message and rapidly selected for responding to the request message.
29. The Ethernet module of claim 27 wherein the communication message is limited to a length that is less than both a TCP transaction length and a maximum transmission unit.
30. The Ethernet module of claim 24 wherein the communication protocol exclusively utilizes a TCP port number 502.
31. The Ethernet module of claim 24 wherein the control processing unit is operably coupled to a factory automation device.

The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.

1. A current source comprising:
a first stage coupled to an input current source, the first stage containing circuitry to receive an input current provided by the input current source;
a second stage coupled to the first stage, the second stage comprising:
a first transistor and a second transistor serially coupled together, wherein a first terminal of the second transistor is coupled to a second terminal of the first transistor;
a third transistor having a first terminal coupled to a third terminal of the first transistor; and
a level shifter coupled to a third terminal of the third transistor and the first terminal of the second transistor, the level shifter containing circuitry to elevate a voltage at a third terminal of the second transistor, wherein the level shifter is arranged in a source-follower configuration.
2. The current source of claim 1, wherein the level shifter comprises a fourth transistor having a first terminal coupled to the third terminal of the third transistor and a third terminal coupled to the first terminal of the second transistor.
3. The current source of claim 2, wherein the first, second, and third transistors are N-type MOSFET (metal-oxide semiconductor field-effect transistors), and wherein the fourth transistor is a P-type MOSFET.
4. The current source of claim 2, wherein a first current source is coupled between a substrate power supply and the first terminal of the third transistor and a second current source is coupled between the substrate power supply and the first terminal of the fourth transistor.
5. The current source of claim 4, wherein the first current source provides a first current that is approximately four times a second current provided by the second current source.
6. The current source of claim 1, wherein the level shifter comprises a plurality of transistors coupled in parallel, wherein each transistor has a first terminal coupled to the third terminal of the third transistor and a third terminal coupled to the first terminal of the second transistor.
7. The current source of claim 6, wherein each transistor in the plurality of transistors are P-type MOSFET (metal-oxide semiconductor field-effect transistors).
8. The current source of claim 6, wherein each transistor in the plurality of transistors have identical geometries.
9. The current source of claim 1, wherein the first stage comprises:
a fifth transistor and a sixth transistor serially coupled together, wherein a first terminal of the sixth transistor is coupled to a second terminal of the fifth transistor;
a seventh transistor having a first terminal coupled to a third terminal of the fifth transistor; and
a second level shifter coupled to a third terminal of the seventh transistor and the first terminal of the sixth transistor, the second level shifter containing circuitry to elevate a voltage at a third terminal of the sixth transistor.
10. The current source of claim 9, wherein the second level shifter is arranged in a source-follower configuration.
11. The current source of claim 9, wherein the second level shifter comprises an eighth transistor having a first terminal coupled to the third terminal of the seventh transistor and a third terminal coupled to the first terminal of the sixth transistor.
12. The current source of claim 11, wherein the fifth, sixth, and seventh transistors are N-type MOSFET (metal-oxide semiconductor field-effect transistors), and wherein the eighth transistor is a P-type MOSFET.
13. The current source of claim 11, wherein a third current source is coupled between a substrate power supply and the first terminal of the seventh transistor and a fourth current source is coupled between the substrate power supply and the first terminal of the eighth transistor.
14. The current source of claim 13, wherein the third current source provides a third current that is approximately four times a fourth current provided by the fourth current source.
15. The current source of claim 9, wherein the first terminal of the fifth transistor is coupled to the input current source.
16. The current source of claim 1, wherein the first terminal is a source terminal, the second terminal is a drain terminal, and the third terminal is a gate terminal.
17. A current source comprising:
a first stage coupled to an input current source, the first stage comprising:
a first transistor and a second transistor serially coupled together, wherein a first terminal of the second transistor is coupled to a second terminal of the first transistor;
a third transistor having a first terminal coupled to a third terminal of the first transistor;
a second level shifter coupled to a third terminal of the third transistor and the first terminal of the second transistor, the second level shifter containing circuitry to elevate a voltage at a third terminal of the second transistor;

the current source further comprising a second stage coupled to the first stage, the second stage comprising:
a fourth transistor and a fifth transistor serially coupled together, wherein a first terminal of the fifth transistor is coupled to a second terminal of the fourth transistor;
a sixth transistor having a first terminal coupled to a third terminal of the fourth transistor; and
a level shifter coupled to a third terminal of the sixth transistor and the first terminal of the fifth transistor, the level shifter containing circuitry to elevate a voltage at a third terminal of the fifth transistor, wherein the level shifter is arranged in a source-follower configuration.
18. The current source of claim 17, wherein the level shifter comprises a seventh transistor having a first terminal coupled to the third terminal of the sixth transistor and a third terminal coupled to the first terminal of the fifth transistor and wherein the second level shifter comprises an eighth transistor having a first terminal coupled to the third terminal of the third transistor and a third terminal coupled to the first terminal of the second transistor.
19. The current source of claim 18, wherein the seventh and the eighth transistors have identical geometries.
20. The current source of claim 17, wherein the level shifter comprises a plurality of transistors coupled in parallel, wherein each transistor has a first terminal coupled to the third terminal of the sixth transistor and a third terminal coupled to the first terminal of the fifth transistor and wherein the second level shifter comprises a second plurality of transistors coupled in parallel, wherein each transistor has a first terminal coupled to the third terminal of the third transistor and a third terminal coupled to the first terminal of the second transistor.
21. The current source of claim 20, wherein each transistor in the plurality of transistors and the second plurality of transistors have identical geometries.
22. The current source of claim 17, wherein the current source is used in a wireless device.
23. A current source comprising:
a first stage coupled to an input current source, the first stage containing circuitry to receive an input current provided by the input current source;
a second stage coupled to the first stage, the second stage comprising:
a first transistor and a second transistor serially coupled together, wherein a first terminal of the second transistor is coupled to a second terminal of the first transistor;
a level shifter coupled to a third terminal of the second transistor and a second terminal of the first transistor, the level shifter containing circuitry to elevate a voltage at the third terminal of the second transistor, wherein the level shifter is arranged in a source-follower configuration; and
a third transistor having a third terminal coupled to the level shifter.
24. The current source of claim 23, wherein the level shifter comprises a fourth transistor having a second terminal coupled to the third terminal of the second transistor and to the third terminal of the third transistor.
25. The current source of claim 24, wherein the first, second, and third transistors are P-type MOSFET (metal-oxide semiconductor field-effect transistors), and wherein the fourth transistor is an N-type MOSFET.
26. The current source of claim 24, wherein a first current source is coupled between a substrate ground and the fourth transistor.
27. The current source of claim 23, wherein the first terminal is a source terminal, the second terminal is a drain terminal, and the third terminal is a gate terminal.