# Patent

## Title
Sequential triggering of series-connected resonant tunneling diodes

## Abstract

One embodiment of the invention includes a quantization circuit. The circuit comprises a sense resistor configured to provide a voltage that is indicative of a digital quantization of an input voltage. The circuit also comprises a plurality of resonant tunneling diodes (RTDs) arranged in series between the input voltage and the sense resistor. The circuit further comprises a sequencing circuit arranged in parallel with the plurality of RTDs and configured to conduct a portion of a current flowing between the input voltage and the sense resistor to define a sequential order of triggering of the plurality of RTDs in response to a given magnitude of the input voltage.

## Background
TECHNICAL FIELD
This invention relates to electronic circuits, and more specifically to sequential triggering of series-connected resonant tunneling diodes.
BACKGROUND
As electronic technology increases, so also does the demand for advances in digital computing technology. One such driving factor includes advances in the technology of devices that convert analog signals to digital signals, and vice verse, such as for implementation in communications devices. A variety of electronic devices that manipulate analog and digital signals can include resonant tunneling diodes (RTDs). An RTD is a non-linear electronic component that can transition from a positive differential resistance region at a lower range of voltages to a positive differential resistance region at a higher range of voltages in a circuit when the voltage across its terminals reaches or exceeds a critical peak value via a quantum tunneling effect.
FIG. 1 illustrates an example of a voltage/current graph 10 of a typical RTD. The graph 10 is a plot of current (I) on the vertical axis versus voltage (V) on the horizontal axis. The current (I) is thus a current flow through the RTD and the voltage (V) is thus a voltage across the RTD.
The graph 10 demonstrates a first region 12, which is a lower positive differential resistance region, that is defined between zero volts and a peak voltage VP. Thus, in the first region 12, the current (I) exhibits a substantially linear relationship relative to an increase in the voltage (V), with a slight leveling near the peak voltage VP to a maximum magnitude of I1. The graph 10 also demonstrates a second region 14, which is a negative differential resistance region, that is defined between the peak voltage VP and a valley voltage VV. The second region 14 is a negative differential resistance region based on a decrease in the current from a magnitude of I1 at the peak voltage VP to a lesser magnitude I2 at the valley voltage VV. The second region 14 can be unstable in a circuit, such that the RTD may not be able to maintain a voltage (V) between the peak voltage VP and the valley voltage VV. The graph 10 also includes a third region 16, which is a higher positive differential resistance region, that begins from the valley voltage VV and increases linearly.
A sequencing device, such as an analog-to-digital converter (ADC), can be designed with a circuit that includes one or more RTDs arranged in series. The one or more RTDs can each be like-sized RTDs with a substantially identical dynamic impedance, such that the circuit can form a series voltage divider. Thus, in response to an input voltage that is applied to the series RTDs, one or more of the RTDs transition, or “trigger”, from the peak voltage VP to the valley voltage VV to provide a quantization of the input voltage. However, since the dynamic impedance is approximately the same for the RTDs, upon applying the input voltage to the series RTDs, two or more of the RTDs can inadvertently be provided with enough voltage to trigger approximately simultaneously. As a result, there may be an error in the quantization of the input voltage.
SUMMARY
One embodiment of the invention includes a quantization circuit. The circuit comprises a sense resistor configured to provide a voltage that is indicative of a digital quantization of an input voltage. The circuit also comprises a plurality of resonant tunneling diodes (RTDs) arranged in series between the input voltage and the sense resistor. The circuit further comprises a sequencing circuit arranged in parallel with the plurality of RTDs and configured to conduct a portion of a current flowing between the input voltage and the sense resistor to define a sequential order of triggering of the plurality of RTDs in response to a given magnitude of the input voltage.
Another embodiment of the invention includes a method for quantizing an input voltage. The method comprises providing a current flow associated with the input voltage through series-connected RTDs and a sense resistor, and diverting a portion of the current flow from each of the series-connected RTDs through a parallel sequencing circuit. The method also comprises controlling a magnitude of the portion of the current flow from each of the series-connected RTDs individually to define a sequential order of triggering of the series-connected RTDs in response to an increasing magnitude of the input voltage. The method further comprises counting a number of transitions of a voltage across the sense resistor relative to a threshold voltage. The transitions can be associated with the triggering of the series-connected RTDs, with the number of transitions corresponding to a magnitude of the input voltage.
Another embodiment of the invention includes a quantization circuit. The circuit comprises means for indicating a digital quantization of an input voltage based on a quantity of a plurality of RTDs that have triggered in response to the input voltage. The plurality of RTDs can be arranged in series between the input voltage and the means for indicating. The circuit also comprises means for diverting a portion of a current flowing between the input voltage and the means for indicating to define a sequential order of triggering of the plurality of RTDs in response to a given magnitude of the input voltage.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an example of a voltage/current graph of a typical resonant tunneling diode (RTD).
FIG. 2 illustrates an example of an RTD quantization circuit in accordance with an aspect of the invention.
FIG. 3 illustrates an example of a timing diagram of an RTD quantization circuit in accordance with an aspect of the invention.
FIG. 4 illustrates another example of an RTD quantization circuit in accordance with an aspect of the invention.
FIG. 5 illustrates another example of an RTD quantization circuit in accordance with an aspect of the invention.
FIG. 6 illustrates a method for quantizing an input voltage in accordance with an aspect of the invention.



DETAILED DESCRIPTION
The present invention relates to electronic circuits, and more specifically to sequential triggering of series-connected resonant tunneling diodes (RTDs). A series connection of RTDs can include a sequencing circuit that is arranged in parallel with the RTDs. The sequencing circuit can be configured to divert a current flow from an input voltage around one or more of the series RTDs and through a sense resistor. The diverted current flow can be incrementally increasing with respect to the RTDs to define a sequential order in which the RTDs trigger in response to an increasing magnitude of the input voltage.
The sequencing circuit can include transistors acting as switches that are arranged in parallel with each of the respective RTDs. The amount of current that is diverted for each of the RTDs can be based on a bias voltage of each of the transistors. As an example, the bias terminal of each of the transistors can be coupled to a current output terminal of the transistor associated with the immediately preceding RTD in the sequential order. As a result, upon the immediately preceding RTD being triggered, the bias voltage of the transistor decreases, causing the amount of current that is diverted through the transistor to decrease. Accordingly, the current flow through the RTD is the next highest, resulting in the RTD being the next to trigger upon the voltage across the RTD exceeding the critical peak voltage VP.
FIG. 2 illustrates an example of an RTD quantization circuit 50 in accordance with an aspect of the invention. The quantization circuit 50 can be configured to provide digital quantization of an input voltage VIN. Therefore, the quantization circuit 50 can be included in any of a variety of quantizing electronic devices, such as an analog-to-digital converter, a counter, or any of a variety of related signal processing devices.
The quantization circuit 50 includes a plurality of RTDs 52 that are arranged in a series connection. In the example of FIG. 2, the RTDs 52 are demonstrated as RTD1 to RTDN, where N is a positive integer. The series connection of the RTDs 52 is arranged between the input voltage VIN and a sense resistor RSENSE. In the example of FIG. 2, the sense resistor RSENSE is configured to provide an indication of a digital quantization of the input voltage VIN, as indicated by a voltage VR across the sense resistor RSENSE. As an example, upon the input voltage VIN being provided to the quantization circuit 50, one or more of the RTDs 52 can trigger. The voltage VR can cross a threshold voltage at each triggering of an RTD 52, such that a number of transitions of the voltage VR across the threshold voltage can indicate the number of RTDs that have triggered in response to the input voltage VIN. Accordingly, the digital quantization of the input voltage VIN can correspond to the number of transitions, and thus the number of triggered RTDs 52.
The quantization circuit 50 also includes a sequencing circuit 54. The sequencing circuit 54 is configured to divert a portion of a current IR that flows from the input voltage VIN and through the sense resistor RSENSE to a negative voltage rail, demonstrated as ground in the example of FIG. 2. Specifically, the sequencing circuit 54 diverts a current IR′ from flowing through the series connection of RTDs 52 and provides an incrementally increasing amount of current back to each of RTDs 52 in the series connection from RTDN to RTD1. As a result, the sequencing circuit 54 can define a sequential order in which the RTDs 52 trigger in response to an increase in the input voltage VIN. As an example, the sequencing circuit 54 can include bypass switches that are individually configured in parallel with the RTDs 52. As a result, the bypass switches can be controlled such that, upon the triggering of an RTD 52 in the sequential order, a change in voltage across the RTD 52 can cause the switch that is in parallel with the next RTD 52 in the sequential order can be deactivated, such that a portion of the current IR is no longer diverted around the next RTD 52 in the sequential order. Accordingly, the increase in current flow through the next RTD 52 causes it to trigger next.
In the example of FIG. 2, the current IR′ is diverted from the series connection of the RTDs 52, with a current IRN flowing through RTDN. The magnitude of the current IR′ can be significantly larger than the current IRN. The sequencing circuit then adds a portion of the current IR′ back to the series connection of the RTDs 52, such that a current IRN′ is added to the current IRN to flow through an RTDN-1 (not shown). A current IR2′ is added to a current IR2 that flows through RTD2, such that a current IR1, which is a sum of the currents IR2 and IR2′, is generated and flows through RTD1. A current IR1′, which is a remaining portion of the current IR′, is added to the current IR1 to thus provide the total current IR at the output of the series connection of RTDs 52, such that the current IR flows through the sense resistor RSENSE and into ground. As a result, the sequencing circuit 54 thus substantially prevents most of the current IR from flowing through the RTDs 52 except for the next RTD 52 in the sequence to trigger as well as the RTDs 52 that have already triggered.
Therefore, it is demonstrated that the RTDs 52 conduct an incrementally decreasing amount of current from RTD1 to RTDN. As a result, the sequencing circuit 54 defines the sequential order of triggering of the RTDs 52 from RTD1 to RTDN based on diverting the portion IR′ of the current IR and providing incrementally decreasing portions of the current IR′ back to the RTDs 52. In addition, upon the triggering of one of the RTDs 52 in the series connection, the sequencing circuit 54 can be configured to adjust the individual portions of the currents provided to the individual RTDs 52, such that the next RTD 52 in the sequential order can be provided more of the diverted current to ensure that it will be the next RTD 52 in the sequential order to trigger. Accordingly, because the RTDs 52 trigger in a sequential order, concurrent triggering of the RTDs 52, such as resulting in a digital quantization error, is substantially mitigated.
FIG. 3 illustrates an example of a timing diagram 80 of an RTD quantization circuit in accordance with an aspect of the invention. The timing diagram 80 can correspond to timing of the RTD quantization circuit 50 in the example of FIG. 2. Therefore, reference is to be made to the example of FIG. 2 in the following description of the example of FIG. 3. In addition, it is to be understood that, in the example of FIG. 3, the quantity N of RTDs 52 is four. Therefore, the example of FIG. 3 describes RTD1 through RTD4, with currents IR1 through IR4 flowing through RTD1 through RTD4, respectively. In addition, it is to be understood that the graph 10 is illustrated as an ideal graph, such that inherent variations in relative magnitudes and/or non-linear characteristics are not demonstrated in the example of FIG. 3.
The timing diagram 80 demonstrates the voltage VR plotted across time. At a time T0, the input voltage VIN begins to increase. Therefore, the voltage VR, which is directly proportional to the current IR, likewise begins to increase. As described above, the sequencing circuit 54 defines the sequential order of triggering based on setting an incrementally increasing magnitude of current through each of the RTDs 52 in the sequential order, such that the current IR1 is greater than the current IR2, which is greater than the current IR3, which is greater than the current IR4.
At a time T1, the current IR1 achieves a magnitude (e.g., I1 in the example of FIG. 1) that is sufficient to trigger RTD1. Upon RTD1 triggering, RTD1 enters a negative differential resistance region, resulting in a decrease of the current IR, and thus a decrease of the voltage VR, indicated in the example of FIG. 3 at 82. In the example of FIG. 3, the decrease of voltage VR occurs very rapidly by an amount that is approximately equal to the valley voltage VV minus the peak voltage VP, and the voltage VR decreases less than a threshold voltage VT. The first decrease of the voltage VR less than the threshold voltage VT thus signals a first digital quantization of the input voltage VIN. In addition, upon RTD1 triggering, the voltage across RTD1 increases by an amount that is approximately equal to the decrease of the voltage VR (i.e., VV minus VP).
Subsequent to the triggering of RTD1, the input voltage VIN continues to increase, resulting in a continued increase of the current IR, and thus a continued increase of the voltage VR. At a time T2, the current IR2 achieves a magnitude that is sufficient to trigger RTD2. Upon RTD2 triggering, RTD2 enters a negative differential resistance region, resulting in a decrease in the current IR, and thus a decrease in the voltage VR less than the threshold voltage VT, indicated in the example of FIG. 3 at 84. The second decrease of the voltage VR less than the threshold voltage VT thus signals a second digital quantization of the input voltage VIN.
Subsequent to the triggering of RTD2, the input voltage VIN continues to increase, resulting in a continued increase of the current IR, and thus a continued increase of the voltage VR. At a time T3, the current IR3 achieves a magnitude that is sufficient to trigger RTD3. Upon RTD3 triggering, RTD3 enters a negative differential resistance region, resulting in a decrease in the current IR, and thus a decrease in the voltage VR less than the threshold voltage VT, indicated in the example of FIG. 3 at 86. The third decrease of the voltage VR less than the threshold voltage VT thus signals a third digital quantization of the input voltage VIN.
Subsequent to the triggering of RTD3, the input voltage VIN continues to increase, resulting in a continued increase of the current IR, and thus a continued increase of the voltage VR. At a time T4, the current IR4 achieves a magnitude that is sufficient to trigger RTD4. Upon RTD4 triggering, RTD4 enters a negative differential resistance region, resulting in a decrease in the current IR, and thus a decrease in the voltage VR less than the threshold voltage VT, indicated in the example of FIG. 3 at 88. The fourth decrease of the voltage VR less than the threshold voltage VT thus signals a fourth and final digital quantization of the input voltage VIN. Accordingly, subsequent to the fourth digital quantization of the input voltage VIN, the voltage VR increases linearly with increases of the input voltage VIN, as indicated in the example of FIG. 3 at 90.
It is thus demonstrated in the example of FIG. 3 that the digital quantization of the input voltage VIN can be ascertained based on a number of negative crossings of the voltage VR relative to the threshold voltage VT. By setting the sequential order of the triggering of the RTDs 52 at distinct times relative to each other, the sequencing circuit 54 thus mitigates concurrent triggering of one or more of the RTDs 52, which could result in an error in the digital quantization of the input voltage VIN. As an example, an error in the digital quantization of the input voltage VIN can occur as a result of a single negative crossing of the voltage VR relative to the voltage VT for the triggering of more than one of the RTDs 52. As a result, based on the sequential triggering of the RTDs 52, an electronic component that is configured to count the negative crossings can identify an appropriate digital quantization of the input voltage VIN substantially without errors.
FIG. 4 illustrates another example of an RTD quantization circuit 100 in accordance with an aspect of the invention. The quantization circuit 100 can be configured to provide digital quantization of an input voltage VIN that is provided from a voltage source 101. Therefore, the quantization circuit 100 can be included in any of a variety of quantizing electronic devices, such as an analog-to-digital converter, a counter, or any of a variety of related signal processing devices.
The quantization circuit 100 includes a plurality of RTDs 102, demonstrated as RTD1 through RTD4 in the example of FIG. 4, that are arranged in a series connection. The series connection of the RTDs 102 is arranged between the input voltage VIN and a sense resistor RSENSE. In the example of FIG. 4, the sense resistor RSENSE is configured to provide an indication of a digital quantization of the input voltage VIN, as indicated by a voltage VR across the sense resistor RSENSE. As an example, upon the input voltage VIN being provided to the quantization circuit 100, one or more of the RTDs 102 can trigger. The voltage VR can cross a threshold voltage at each triggering of an RTD 102, such that a number of transitions of the voltage VR across the threshold voltage can indicate the number of RTDs that have triggered in response to the input voltage VIN. Accordingly, the digital quantization of the input voltage VIN can correspond to the number of transitions, and thus the number of triggered RTDs 102.
The quantization circuit 100 also includes a sequencing circuit 104. The sequencing circuit 104 is configured to divert a portion of a current IR that flows from the input voltage VIN and through the sense resistor RSENSE to a negative voltage rail, demonstrated as ground in the example of FIG. 4. Specifically, the sequencing circuit 104 diverts a current IR′ from flowing through the series connection of RTDs 102 and provides an incrementally increasing amount of current back to each of RTDs 102 in the series connection from RTD4 to RTD1. As a result, the sequencing circuit 104 can define a sequential order in which the RTDs 102 trigger in response to an increase in the input voltage VIN. Specifically, in the example of FIG. 4, the sequential order is defined as the triggering of RTD1, followed by RTD2, followed by RTD3, followed by RTD4 in response to an increasing magnitude of the input voltage VIN.
The sequencing circuit 104 includes a plurality of bypass transistors 106, demonstrated in the example of FIG. 4 as N1 through N4. In the example of FIG. 4, the bypass transistors 106 are demonstrated as N-type field effect transistors (N-FETs), and can be configured as depletion-mode transistors. As an example, the bypass transistors 106 can be Gallium Arsenide (GaAs) MESFET transistors. However, it is to be understood that the quantization circuit 100 is not limited to the use of depletion-mode N-FETs, but could include any of a variety of transistors. Each of the bypass transistors 106 is configured in parallel with a respective one of the RTDs 102, such that the transistor N1 is configured in parallel with RTD1, the transistor N2 is configured in parallel with RTD2, the transistor N3 is configured in parallel with RTD3, and the transistor N4 is configured in parallel with RTD4. Therefore, each of the bypass transistors 106 is configured to conduct a portion of the current IR′, and thus divert a portion of the current IR, based on a relative bias of each of the bypass transistors 106 to define a sequential order of triggering of each of the RTDs 102.
The bias of each of the bypass transistors 106 is set based on coupling the bias terminal (i.e., gate) to a current output terminal (i.e., source) of the bypass transistor 106 associated with the immediately preceding RTD 102 in the sequential order. Specifically, the transistor N4 has a gate coupled to a source of the transistor N3, the transistor N3 has a gate coupled to a source of the transistor N2, and the transistor N2 has a gate coupled to a source of the transistor N1. The transistor N1 has a gate coupled to a bias voltage source 108 that applies a programmable bias voltage VBIAS to the gate of the transistor N1. As an example, the magnitude of the bias voltage VBIAS can be set to adjust the magnitude of the voltage VIN at which the first RTD 102 in the sequential order (i.e., RTD1) triggers. Specifically, the bias voltage VBIAS can set a resistance magnitude of the transistor N1 to provide precise control of the amount of current that is diverted from RTD1.
As an example, based on the coupling of the gates of the bypass transistors 106 to the sources of the respective bypass transistors 106 of the immediately preceding RTD 102 in the sequential order, the bypass transistors 106 can operate in a linear mode. Specifically, each can conduct an incrementally decreasing amount of current from the transistor N4 to the transistor N1, such that the current flowing through the RTDs 102 is incrementally increasing from RTD4 to RTD1. Described in another manner, the bias of the bypass transistors 106 is such that the current flow through the RTDs 102 is incrementally decreasing in the sequential order of triggering based on an incrementally increasing current that is diverted through the respective bypass transistors 106. As another example, the bypass transistors 106 can act as switches over a non-linear range with substantially greater changes in the current IR. Additionally, as demonstrated in the example of FIG. 4, since the bypass transistors 106 can be configured as depletion-mode transistors, they can conduct current with a negative gate-source voltage VGS.
The current IR′ is diverted from the series connection of the RTDs 102 to flow through the transistor N4, with a current IR4 flowing through RTD4. The magnitude of the current IR′ can be significantly larger than the current IR4 based on a larger bias (i.e., less negative VGS). The sequencing circuit then adds a portion of the current IR′ back to the series connection of the RTDs 52, such that a current IR4′ is provided from the current output from the transistor N4 and is added to the current IR4 to flow through RTD3. Thus, the transistor N3 conducts a magnitude of current of IR′-IR4′, which is less current than that conducted by the transistor N4. However, RTD3 conducts a current IR3 of magnitude IR4+IR4′, which is greater than the current IR4 that flows through RTD4. The transistor N2 thus conducts a current of magnitude IR′−IR4′−IR3′, and the transistor N1 thus conducts a current of magnitude IR′−IR4′−IR3′−IR2′. However, RTD2 conducts a current IR2 of magnitude IR3+IR3′, and RTD1 thus conducts a current IR1 of magnitude IR2+IR2′, respectively. Therefore, the sense resistor RSENSE receives the entirety of the current IR, which is a sum of the currents IR1 and IR1′, such that the current IR flows through the sense resistor RSENSE and into ground.
In addition, as demonstrated in the graph 10 of the example of FIG. 1, upon a given one of the RTDs 102 triggering, the voltage across the given RTD 102 increases rapidly from the peak voltage VP to the valley voltage VV based on the negative differential resistance region 14 being unstable. As a result, based on the coupling of the gates of the bypass transistors 106 to the sources of the respective bypass transistors 106 of the immediately preceding RTD 102 in the sequential order, the gate-source voltage VGS of the next bypass transistor 106 in the sequential order decreases (i.e., becomes more negative). Therefore, the next bypass transistor 106 in the sequential order begins to conduct less current or deactivates entirely (i.e., enters cutoff mode). As a result, the respective next RTD 102 in the sequential order conducts more current, thus further ensuring that it will trigger next in the sequential order for increasing magnitudes of the input voltage VIN.
It is thus demonstrated that the current flow through the bypass transistors 106 continues to incrementally decrease from the transistor N4 to the transistor N1 and the current flow through the RTDs 102 continues to incrementally increase from RTD4 to RTD1. It is also thus demonstrated that the triggering of the RTDs 102 adjusts the bias of the bypass transistors 106 of the subsequent RTDs 102 in the sequential order. Accordingly, the sequential order of triggering of the RTDs 102 is based on the relative magnitudes of current that flow through the RTDs 102 in response to increasing magnitudes of the input voltage VIN. As a result, the voltage VR can be monitored for transitions relative to a threshold voltage VT to obtain a digital quantization of the input voltage VIN that is substantially free from quantization errors.
It is to be understood that the quantization circuit 100 is not intended to be limited to the example of FIG. 4. As an example, the input voltage VIN can be provided as a negative voltage that draws the current IR from RTD1, such that the locations of the voltage source 101 and the sense resistor RSENSE can be swapped. As another example, the bias voltages of each of the bypass transistors 106 can be individually controlled, as opposed to interconnected to the source of the bypass transistor 106 of the immediately preceding RTD 102 in the sequential order. Furthermore, because RTD1 can be designated the first of the RTDs 102 in the sequential order to trigger, the transistor N1 and the bias voltage source 108 could be omitted, such that none of the current IR is diverted from RTD1, even in an untriggered state. Accordingly, the quantization circuit 100 can be configured in any of a variety of ways.
FIG. 5 illustrates another example of an RTD quantization circuit 150 in accordance with an aspect of the invention. The quantization circuit 150 can likewise be configured to provide digital quantization of an input voltage VIN that is provided from a voltage source 151. Therefore, the quantization circuit 150 can be included in any of a variety of quantizing electronic devices, such as an analog-to-digital converter, a counter, or any of a variety of related signal processing devices.
The quantization circuit 150 includes a plurality of RTDs 152, demonstrated as RTD1 through RTD4 in the example of FIG. 5, that are arranged in a series connection, and a sequencing circuit 154. Therefore, the quantization circuit 150 is configured similar to the quantization circuit 100 in the example of FIG. 4. However, in the example of FIG. 5, the input voltage VIN is negative, such that the current IR that flows through the sense resistor RSENSE is provided from ground. Accordingly, the sequencing circuit 154 includes a respective plurality of bypass transistors 156, depicted as P1 through P4, respectively, that are demonstrated in the example of FIG. 5 as depletion-mode P-type field effect transistors (P-FETs). The transistor P1 is demonstrated in the example of FIG. 5 as having a gate coupled to a bias voltage source 158 that applies a programmable bias voltage VBIAS to the gate of the transistor P1.
In the example of FIG. 5, based on the negative potential of the input voltage VIN relative to ground, and based on the inclusion of P-type bypass transistors 156, the polarities are reversed for the currents flowing through the RTDs 152, the currents flowing through the bypass transistors 156, the gate-source voltage VGS of each of the bypass transistors 156, and the voltage VR. Otherwise, the quantization circuit 150 operates substantially the same as the quantization circuit 100 described above in the example of FIG. 4. Specifically, the current flow through the RTDs 152 incrementally decreases from RTD1 through RTD4 based on an incrementally increasing current flow through the bypass transistors 156 from the transistor P1 through the transistor P4, respectively. Accordingly, the sequencing circuit 154 defines a sequential order of triggering of the RTDs 152 from RTD1 through RTD4, similar to as described above in the example of FIG. 4.
It is to be understood that the quantization circuit 150 is not intended to be limited to the example of FIG. 5. As an example, the input voltage VIN can be provided as a positive voltage that provides the current IR to RTD1, such that the locations of the voltage source 151 and the sense resistor RSENSE can be swapped. As another example, the bias voltages of each of the bypass transistors 156 can be individually controlled, as opposed to interconnected to the source of the bypass transistor 156 of the immediately preceding RTD 152 in the sequential order. Accordingly, the quantization circuit 150 can be configured in any of a variety of ways.
In view of the foregoing structural and functional features described above, certain methods will be better appreciated with reference to FIG. 6. It is to be understood and appreciated that the illustrated actions, in other embodiments, may occur in different orders and/or concurrently with other actions. Moreover, not all illustrated features may be required to implement a method.
FIG. 6 illustrates a method 200 for quantizing an input voltage in accordance with an aspect of the invention. At 202, a current flow associated with the input voltage is provided through series-connected RTDs and a sense resistor. The input voltage can be positive, such that the current is provided from the input voltage, or negative, such that the current is provided from a negative voltage rail. The sense resistor can be a resistor having a voltage that is indicative of the quantization of the input voltage. At 204, a portion of the current flow is diverted from each of the series-connected RTDs through a parallel sequencing circuit. The parallel sequencing circuit can include a transistor associated with each of the RTDs, with each transistor being configured to conduct the diverted portion of the current flow.
At 206, a magnitude of the portion of the current flow diverted from each of the series-connected RTDs is individually controlled to define a sequential order of triggering of the series-connected RTDs in response to an increasing magnitude of the input voltage. The magnitude can be controlled based on setting the bias of the transistors to set an incrementally decreasing magnitude of current flowing through each of the RTDs in the sequential order based on diverting an incrementally increasing current through the transistors associated with each of the respective RTDs. The bias terminals of the transistors can be coupled to a current output terminal of the transistors of the immediately preceding RTDs in the sequential order, such that upon the immediately preceding RTD triggering, the current flow through the next RTD increases to ensure that it will trigger next.
At 208, a number of transitions are counted of a voltage across the sense resistor relative to a threshold voltage. The transitions can be associated with the triggering of the series-connected RTDs, with the number of transitions corresponding to a magnitude of the input voltage. The digital quantization of the input voltage can thus correspond to the number of transitions. Thus, the sequential triggering of the RTDs can be implemented in quantization of an input voltage in a counter, ADC, or any of a variety of other signal processing devices.
What have been described above are examples of the invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the invention are possible. Accordingly, the invention is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims.

## Claims

1. A quantization circuit comprising:
a sense resistor configured to provide a voltage that is indicative of a digital quantization of an input voltage;
a plurality of resonant tunneling diodes (RTDs) arranged in series between the input voltage and the sense resistor; and
a sequencing circuit arranged in parallel with the plurality of RTDs and configured to conduct a portion of a current flowing between the input voltage and the sense resistor to define a sequential order of triggering of the plurality of RTDs in response to a given magnitude of the input voltage.

2. The circuit of claim 1, wherein the sequencing circuit is configured to set an incrementally decreasing amount of the current conducted through each of the plurality of RTDs relative to each other to define the sequential order of triggering.

3. The circuit of claim 1, wherein the sequencing circuit comprises a plurality of transistors, each of the transistors being associated with a respective one of the plurality of RTDs and configured to control an amount of the current flowing through the respective one of the plurality of RTDs.

4. The circuit of claim 3, wherein each of the plurality of transistors is arranged in parallel with the respective one of the plurality of RTDs, the amount of current flowing through the respective one of the plurality of RTDs being based on a magnitude of a voltage at a bias terminal of an associated one of the plurality of transistors.

5. The circuit of claim 3, wherein each of the transistors comprises a bias terminal coupled to a current output terminal of an immediately preceding RTD in the sequential order, and comprises a current output terminal coupled to a current input terminal of the immediately preceding RTD in the sequential order, such that a voltage between the bias terminal and the current output terminal of a given one of the transistors is set to increase the amount of current flowing through a respective one of the RTDs upon the immediately preceding RTD being triggered.

6. The circuit of claim 5, wherein, upon the immediately preceding RTD in the sequential order being triggered, the voltage between the bias terminal and the current output terminal of the given one of the transistors is increased to substantially deactivate the given one of the transistors.

7. The circuit of claim 3, wherein the sequencing circuit comprises a voltage source configured to provide a bias voltage to a bias terminal of a given one of the plurality of transistors associated with a respective one of the plurality of RTDs that is first in the sequential order, the bias voltage having a magnitude that is set to define a magnitude of the input voltage at which the respective one of the plurality of RTDs triggers.

8. The circuit of claim 3, wherein the plurality of transistors are depletion-mode field effect transistors.

9. The circuit of claim 1, wherein the input voltage has a negative magnitude.

10. An analog-to-digital converter comprising the sequencing circuit of claim 1.

11. A method for quantizing an input voltage, the method comprising:
providing a current flow associated with the input voltage through series-connected resonant tunneling diodes (RTDs) and a sense resistor;
diverting a portion of the current flow from each of the series-connected RTDs through a parallel sequencing circuit;
controlling a magnitude of the portion of the current flow from each of the series-connected RTDs individually to define a sequential order of triggering of the series-connected RTDs in response to an increasing magnitude of the input voltage; and
counting a number of transitions of a voltage across the sense resistor relative to a threshold voltage, the transitions being associated with the triggering of the series-connected RTDs, the number of transitions corresponding to a magnitude of the input voltage.

12. The method of claim 11, wherein controlling the magnitude of the portion of the current flow comprises individually setting a magnitude of a bias voltage for a plurality of transistors that are each configured in parallel with a respective one of the series-connected RTDs.

13. The method of claim 12, wherein individually setting the magnitude of the bias voltage comprises setting the magnitude of the bias voltage for each of the plurality of transistors to divert an incrementally increasing amount of the current conducted through each of the plurality of transistors relative to each other to define the sequential order of triggering of the series-connected RTDs.

14. The method of claim 12, wherein controlling the magnitude of the portion of the current flow comprises decreasing the magnitude of the bias voltage of a given one of the transistors to increase the amount of current flowing through a respective one of the RTDs upon the immediately preceding RTD in the sequential order being triggered.

15. The method of claim 14, further comprising:
coupling a bias terminal of a given one of the transistors to a current output terminal of a transistor associated with an immediately preceding RTD in the sequential order;
wherein decreasing the magnitude of the bias voltage comprises decreasing the bias voltage in response to a decrease in a voltage associated with the current output terminal of the transistor associated with the immediately preceding RTD upon the immediately preceding RTD in the sequential order being triggered.

16. The method of claim 12, further comprising:
providing a bias voltage to a bias terminal of a given one of the plurality of transistors associated with a respective one of the plurality of RTDs that is first in the sequential order; and
setting the bias voltage having a magnitude that is set to define a magnitude of the input voltage at which the respective one of the plurality of RTDs triggers.

17. A quantization circuit comprising:
means for indicating a digital quantization of an input voltage based on a quantity of a plurality of resonant tunneling diodes (RTDs) that have triggered in response to the input voltage, the plurality of RTDs being arranged in series between the input voltage and the means for indicating; and
means for diverting a portion of a current flowing between the input voltage and the means for indicating to define a sequential order of triggering of the plurality of RTDs in response to a given magnitude of the input voltage.

18. The circuit of claim 17, wherein the means for diverting comprises individual means for diverting an incrementally decreasing amount of the current conducted through each of the respective plurality of RTDs relative to each other to define the sequential order of triggering of the current from each of the plurality of RTDs.

19. The circuit of claim 18, wherein a given one of the plurality of RTDs begins to conduct a greater amount of current in response to a triggering of an immediately preceding one of the plurality of RTDs in the sequential order.

20. The circuit of claim 17, wherein the means for diverting comprises means for setting a magnitude of the input voltage at which a first of the plurality of RTDs triggers in the sequential order.