Processing control signals using a level shifting circuit

Abstract

LEDs may be connected in a series string fed by a constant current supply (figure 2). Control signals may operate switch transistors that bypass individual LEDs. However, as LEDs are switched in and

Description

Technical Field

[0001] The present disclosure concerns processing control signals. More particularly, but not exclusively, this disclosure concerns methods, apparatus and circuitry for processing control signals using a level shifting circuit. Background

[0002] Various electronic devices may be controlled on the basis of control signals. Such control signals may be used to switch an electronic device from an activated state to a deactivated state and vice-versa. An example of such a device comprises a light-emitting diode, LED, and a bypass transistor (or ‘switch’) arranged in parallel with the LED. The LED may be ‘turned off’ by applying a given voltage across the transistor using a control signal. Similarly, turning the transistor ‘off’ via a control signal acts to place a voltage across the LED sufficient to turn the LED ‘on’.

[0003] For some electronic devices, the voltage required to control the electronic device (e.g. to switch a transistor from an ‘off state to an ‘on’ state, or vice-versa) may be variable, and may depend on various operating conditions, such as environmental conditions, e.g. temperature, and / or the operating states of other electronic devices that are electrically connected to the electronic device. Further, the voltage required to control the electronic device may be relatively high in some cases, e.g. for an electronic device comprising multiple individually-switchable LEDs or other components connected in series. Implementing a system that can provide and withstand such high voltages may be difficult.

[0004] The present disclosure seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present disclosure seeks to provide an improved circuit, apparatus and / or method for processing control signals for electronic devices. Summary

[0005] The present disclosure provides, according to a first aspect, apparatus comprising a level shifting circuit configured to: receive a control signal operable to control an electronic device, the control signal having either a first voltage for switching the electronic device from a deactivated state to an activated state or a second voltage for switching the electronic device from the activated state to the deactivated state, the first voltage and the second voltage defining respective endpoints of a voltage range of the control signal; shift each endpoint of the voltage range of the control signal by a voltage offset to generate a level shifted control signal; and output the level shifted control signal to control the electronic device.

[0006] According to a second aspect of the disclosure there is also provided a method of processing control signals using a level shifting circuit, the method comprising, at the level shifting circuit: receiving a control signal operable to control an electronic device, the control signal having either a first voltage for switching the electronic device from a deactivated state to an activated state or a second voltage for switching the electronic device from the activated state to the deactivated state, the first voltage and the second voltage defining respective endpoints of a voltage range of the control signal; shifting each endpoint of the voltage range of the control signal by a voltage offset to generate a level shifted control signal; and outputting the level shifted control signal to control the electronic device.

[0007] According to a third aspect of the disclosure there is also provided circuitry comprising a plurality of logic inverters connected in series, each of the plurality of logic inverters being arranged to receive a different supply voltage, the circuitry being configured to: receive a control signal operable to control an electronic device, the control signal having either a first voltage for switching the electronic device from a deactivated state to an activated state or a second voltage for switching the electronic device from the activated state to the deactivated state, the first voltage and the second voltage defining respective endpoints of a voltage range of the control signal; process the control signal using at least one logic inverter of the plurality of logic inverters to generate a level shifted control signal, each of the plurality of logic inverters being configured to offset each endpoint of the voltage range of the control signal by a given voltage; and output the level shifted control signal to control the electronic device.

[0008] It will of course be appreciated that features described in relation to one aspect of the present disclosure may be incorporated into other aspects of the present disclosure. For example, the method of the disclosure may incorporate any of the features described with reference to the apparatus of the disclosure and vice versa. Description of the Drawings

[0009] Embodiments of the present disclosure will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows a schematic view of an apparatus according to the present disclosure; Figure 2 shows a circuit diagram of an example electronic device according to the present disclosure; Figure 3 shows a circuit diagram of an example level shifting circuit according to the present disclosure; Figure 4 shows the results of a simulation of a level shifting circuit according to the present disclosure; Figure 5 shows a flow diagram illustrating the steps of a method according to the present disclosure; and Figure 6 shows a schematic view of circuitry according to the present disclosure. Detailed Description

[0010] Figure 1 shows a schematic view of an apparatus 100 according to the present disclosure. The apparatus 100 comprises electronic circuitry 110 configured to process signals, as will be described below. In particular, the electronic circuitry 110 comprises a level shifting circuit configured to process control signals. The electronic circuitry 110 may comprise all or part of an integrated circuit.

[0011] The level shifting circuit 110 is configured to receive a control signal 120 operable to control an electronic device 150. The electronic device 150 is switchable between an activated state and a deactivated state. That is, the electronic device 150 may be switched from the activated state to the deactivated state and / or vice-versa. In the example shown in Figure 1, the apparatus 100 comprises the electronic device 150. For example, the level shifting circuit 110 and the electronic device 150 may be arranged on the same substrate. Alternatively, the electronic device 150 may be separate from the apparatus 100. For example, the level shifting circuit 110 and the electronic device 150 may be arranged on different substrates and / or may be implemented by different integrated circuits. Accordingly, it will be understood that the electronic device 150 may be omitted from the apparatus 100 in some examples.

[0012] The received control signal 120 has either a first voltage for switching the electronic device 150 from the deactivated state to the activated state, or a second voltage for switching the electronic device 150 from the activated state to the deactivated state. The control signal 120 may also be referred to as a ‘drive signal’. It will be understood that whether the control signal 120 has the first voltage or the second voltage may be time-dependent. That is, the control signal 120 may have the first voltage during a first time interval and the second voltage during a second time interval. The control signal 120 may thus take both values (the value of the first voltage and the value of the second voltage) at different times. In other words, the voltage of the control signal 120 may not be fixed at either the first voltage or the second voltage, but may switch between the two. Switching of the control signal 120 from the first voltage to the second voltage or vice-versa may be intended to cause the electronic device 150 to be activated and / or deactivated. For example, when it is desired to switch the electronic device 150 from the deactivated state to the activated state, the voltage of the control signal may be switched from the second voltage to the first voltage, or vice-versa.

[0013] The first voltage and the second voltage define respective endpoints of a voltage range of the control signal 120. For example, the first voltage may be 3V and the second voltage may be 0V, and therefore the voltage range of the received control signal 120 may be 0-3V. In another example, the first voltage may be 5V and the second voltage may be 0V, and therefore the voltage range may be 0-5V. It will be understood that the first voltage, second voltage and / or voltage range of the control signal 120 may take other values. One of the first voltage and the second voltage may be zero volts (or ‘ground’). Alternatively, neither of the first voltage and the second voltage may be zero volts.

[0014] The level shifting circuit 110 is configured to shift each endpoint of the voltage range of the control signal 120 by a voltage offset, to generate a level shifted control signal 130. The level shifting circuit 110 is also configured to output the level shifted control signal 130 to control the electronic device 150. As such, the level shifting circuit 110 is configured to receive a control signal 120 as an input and to output a level shifted control signal 130. This enables the control signal to be adapted to suit a wider variety of electronic devices, in different configurations and / or arrangements, and / or in different dynamic conditions, which may require (or perform better with) control signals having different voltage ranges. Further, shifting the endpoints of the voltage range of the control signal 120 may reduce the requirements of the electronic device, e.g. in terms of the voltages that the device is required to withstand. This is discussed in more detail below.

[0015] The level shifted control signal 130 has a voltage range that is shifted relative to the voltage range of the input control signal 120. For example, the voltage range of the input control signal 120 may be 0-3V and the voltage range of the level shifted control signal 130 may be 5-8V. In some cases, the voltage range of the level shifted control signal 130 may overlap with the voltage range of the input control signal 120. For example, the voltage range of the input control signal 120 may be 0-5V and the voltage range of the level shifted control signal 130 may be 3-8V. Alternatively, the voltage range of the level shifted control signal 130 may be non-overlapping with the voltage range of the input control signal 120. The voltage range of the level shifted control signal 130 may be dynamic, e.g. time-varying. For example, the voltage range of the level shifted control signal 130 may be dependent on a current operating condition and / or state of the electronic device or of other electronic devices connected thereto.

[0016] The level shifting circuit 110 may comprise one or more logic inverters, as will be described in more detail below, e.g. with reference to Figure 3. A logic inverter is configured to perform an inversion of a voltage between two levels, typically (but not exclusively) a few volts apart. It will be understood that a “logic 5 inverter” as described herein may not be a logic circuit, but rather is an inverter that is configured to switch between logic-level voltages, e.g. from an initial voltage to a subsequent offset voltage.

[0017] In particular, but not exclusively, the level shifting circuit 110 may comprise a plurality of logic inverters connected in series. In some cases, each logic inverter in the plurality of logic inverters is configured to receive a different supply voltage. This allows the chain of logic inverters to incrementally shift the voltage range of the input control signal by a desired amount. As such, the level shifting circuit 110 is able to apply different voltage offsets to the input control signal, thereby producing level shifted control signals having different voltage ranges relative to the input control signal. Additionally or alternatively, each logic inverter in the plurality of logic inverters is configured to receive a respective driving supply voltage and a respective ground supply voltage, and each logic inverter in the plurality of logic inverters is configured to receive a different ground supply voltage. Accordingly, each logic inverter in the plurality of logic inverters may receive both a different driving supply voltage and a different ground supply voltage. Alternatively, each logic inverter may receive a different driving supply voltage but the same ground supply voltage, or each logic inverter may receive the same driving supply voltage but a different ground supply voltage.

[0018] As mentioned above, the level shifting circuit 110 is configured to shift each endpoint of the voltage range of a control signal 120 by a voltage offset to generate a level shifted control signal 130. The voltage offset (and thus the voltage range of the level shifted control signal 130) may be dependent on an operating condition of the electronic device 150. The operating condition may comprise one or more of: whether the electronic device 150 is in the activated state or the deactivated state, an operating temperature of the electronic device 150, an operating current of the electronic device 150, or an operating state of a further electronic device. The voltage offset may be dependent on other operating conditions in other examples, for example an amount of noise in a power supply of the control signal. Therefore, the voltage offset (and thus the voltage range of the level shifted control signal 130) may be adapted to the dynamic operating conditions associated with the electronic device 150. This allows the control signal to control the electronic device 150 under a wider variety of conditions and / or configurations. Alternatively, the voltage offset may be independent of an operating condition of the electronic device 150. That is, the same voltage offset may be applied regardless of the operating condition of the electronic device 150.

[0019] Additionally or alternatively, the voltage offset is dependent on a source voltage and / or a drain voltage of the electronic device 150. This will be described further, below.

[0020] The level shifted control signal 130 generated by the level shifting circuit 110 may be at a driving voltage for the electronic device 150 or a ground voltage for the electronic device 150. For example, when the control signal 120 has the first voltage (e.g. 3V), the resulting level shifted control signal 130 may be at a driving voltage for the electronic device 150 (e.g. 15V), and when the control signal 120 has the second voltage (e.g. 0V), the resulting level shifted control signal 130 may be at a ground voltage for the electronic device 150 (e.g. 12V). It should be noted that the ground voltage for the electronic device 150 may be non-zero, because both endpoints of the voltage range of the control signal 120 are shifted by the level shifting circuit 110, not just the upper endpoint. That is, the ground voltage is shifted by the level shifting circuit 110 in addition to the driving voltage.

[0021] The electronic device 150 may comprise a transistor. The transistor may be arranged on the same substrate and / or in the same integrated circuit, IC, as the level shifting circuit 110. Additionally or alternatively, the electronic device 150 may comprise a light emitting diode, LED. Again, the LED may be arranged on the same substrate and / or in the same IC as the level shifting circuit 110. The control signal may be operable to change a state of a bypass transistor connected in parallel with the LED. For example, outputting the level shifted control signal 130 may comprise outputting the level shifted control signal 130 to a gate of the bypass transistor. This causes the state of the bypass transistor to change, thereby changing the activation state of the LED (e.g. switching the LED ‘on’ or ‘off’). Additionally or alternatively, the electronic device 150 may comprise a plurality of LEDs connected in series. Such an example electronic device is shown in Figure 2. A more detailed explanation of the components shown in Figure 2 is given below. In some such cases, the voltage offset may be dependent on a voltage at a common connection of a first LED of the plurality of LEDs and a second LED of the plurality of LEDs (e.g. at node G or node B shown in Figure 2). Additionally or alternatively, the electronic device 150 may comprise a pixel array or a memory array. In such devices, the power supply may be variable across the array, e.g. whereby one end of the array draws current which affects the rest of the array. Other examples of electronic device 150 for which the presently-described methods can be applied are envisaged, which do not involve LEDs. For example, the electronic device 150 may comprise one or more motors and / or speakers. Such motors and / or speakers may be arranged in a series configuration with a current sink. More generally, the electronic device 150 may comprise any device that is controllable via a drive or control signal, and in particular where voltages at nodes between components may vary over time. Such variations in local circuit voltages may affect the control signal voltage required to control the electronic device 150. Processing the control signal using the level shifting circuit 110 described herein enables such variations in local circuit voltages to be compensated for.

[0022] The voltage offset may be the same for each endpoint of the voltage range of the control signal 120. That is, both endpoints of the voltage range may be shifted by the same amount, e.g. 0-3V may be shifted to 2-5V. Alternatively, different voltage offsets may be applied to the two endpoints of the voltage range, e.g. 0-3V may be shifted to 2-6V.

[0023] In examples where the level shifting circuit 110 comprises circuitry comprising a plurality of logic inverters connected in series, the shifting of the endpoints of the voltage range of the control signal 120 may comprise processing the control signal 120 using at least one of the plurality of logic inverters, where each of the plurality of logic inverters is configured to offset each endpoint of the voltage range of the control signal 120 by a given voltage. The control signal 120 may be processed by all of the plurality of logic inverters in some cases. For example, an initial control signal having a voltage range of 0-3V may be processed by a first logic inverter, which applies an offset of 5V to the endpoints of the voltage range, thereby shifting the voltage range of the control signal to 5-8V. This ‘intermediate’ control signal may then be processed by a second logic inverter, which also applies an offset of 5V to the endpoints of the voltage range, thereby further shifting the voltage range of the control signal to 10-13V. The control signal may then be processed by further logic inverters (to further shift the voltage range of the control signal) or may be outputted to control the electronic device. Accordingly, an incremental voltage shift may be provided, wherein the number of logic inverters of the plurality of logic inverters which process the control signal 120 affects the resulting overall voltage shift. Different logic inverters of the plurality of logic inverters may be configured to apply the same incremental voltage offset or different incremental voltage offsets to one another.

[0024] The apparatus 100 may comprise or be comprised on a flexible integrated circuit. Flexible integrated circuits are generally much thinner and more flexible than conventional integrated circuits, enabling them to be used in a wider range of applications. In accordance with the present disclosure a “flexible integrated circuit” (flexible IC or flexIC) is a type of integrated circuit, IC, that is designed to be flexible and conformable, allowing it to bend, twist, and conform to non-flat or irregular surfaces. Unlike traditional rigid ICs, which are typically made on silicon wafers and are inflexible, flexible ICs, in accordance with the present disclosure, are fabricated on flexible substrates using appropriate materials and thin-film processes. The flexible IC may comprise a thin film IC. The flexible IC may comprise an IC formed from thin films on an insulating substrate. As such, the apparatus 100 may comprise or be comprised on an integrated circuit formed from thin films on an insulating substrate. Flexible integrated circuits (comprising insulating substrates) may be particularly suited for use as the apparatus 100 comprising the level shifting circuit 110, e.g. because such circuits do not have to be grounded to 0V, unlike silicon-based integrated circuits. Therefore, as described herein, both endpoints (including the ‘ground’ voltage as well as the ‘driving’ voltage) of the control signal voltage range may be offset by the level shifting circuit 110. Such a solution may be difficult to implement with a silicon-based integrated circuit, but a flexible integrated circuit, e.g. formed from thin films on an insulating substrate, allows for such an implementation.

[0025] The insulating substrate is typically formed of an appropriate flexible polymer material. Nevertheless, the flexible substrate may be formed from any other materials that provide suitable electrical, chemical, and / or structural properties. The flexible substrate may be formed from a single common material, may be formed from a plurality of different materials, or may be formed from a plurality of different types of the same material (e.g. different polymers). The flexible substrate may, for example, comprise one or more materials selected from the following list of materials: flexible glass, polymer materials, metal oxide materials, resin materials, resist materials, foil materials, paper, insulator coated metals, or any other suitable material.

[0026] Where a polymer based material is used, the substrate may comprise one or more polymers selected from: polyethylene naphthalates, polyethylene terephthalates; polymethyl methacrylates; polycarbonates, polyvinyl alcohols, polyvinyl acetates, polyvinyl pyrrolidones, polyvinyl phenols, polyvinyl chlorides, polystyrenes, polyimides, polyamides (e.g. Nylon); poly(hydroxy ethers), polyurethanes, polycarbonates, polysulfones, parylenes, polyarylates, polyether ether ketones (PEEKs); acrylonitrile butadiene styrene (ABS), 1 Methoxy 2 propyl acetates, Benzocyclobutenes (BCB), polylactic acid (PLA), polyhydroxyalkanoates (PHAs), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), cellulose polymers, or any other suitable polymer material.

[0027] Where a metal oxide based material is used, the substrate may comprise one or more metal oxides selected from: AI2O3, SiOxNy, SiO2, Si3N4, or any other suitable metal oxide. Where a resin based material is used, the substrate may comprise one or more resins selected from: a UV-curable resin or any other suitable resin. Where a resist based material is used, the substrate may comprise one or more resists selected from: nanoimprint resists, photoresists such as, for example, Bisphenol A novolac epoxy (SU-8) or poly hydroxy benzyl silsesquioxane, or any other suitable resist. Where a foil based material is used the substrate may comprise one or more foils selected from: polymeric foils or any other suitable foil. Where an insulator-coated metal is used, the substrate may comprise one or more insulator-coated metals selected from: insulator coated stainless-steel or any other suitable insulator-coated metal.

[0028] Alternatively, the apparatus 100 does not comprise a flexible IC or an insulating substrate. For example, the apparatus 100 may comprise a silicon-based device.

[0029] The apparatus 100 may be configured to receive the voltage offset from a voltage mirror circuit (not shown). This is described in more detail below. The voltage mirror circuit may be configured to duplicate a source voltage and / or a drain voltage of the electronic device. For example, the voltage mirror circuit may be configured to duplicate a voltage at a node between components that are connected in series in the electronic device, e.g. a local circuit voltage. In some examples, the apparatus 100 comprises the voltage mirror circuit. That is, the level shifting circuit 110 and the voltage mirror circuit may be arranged on the same substrate (e.g. a flexible substrate of a flexible IC). Alternatively, the voltage mirror circuit may be separate from the apparatus 100. For example, the level shifting circuit 110 and the voltage mirror circuit may be arranged on different substrates. Alternatively, the voltage offset is not received from a voltage mirror circuit, and a voltage mirror circuit may therefore be omitted in some cases.

[0030] The apparatus 100 may comprise a second level shifting circuit (not shown) in addition to the level shifting circuit 110. For example, the level shifting circuit 110 may be a first level shifting circuit, the voltage offset may be a first voltage offset, the level shifted control signal 130 is a first level shifted control signal, and the electronic device 150 is a first electronic device. The second level shifting circuit may be configured to receive a second control signal operable to control a second electronic device. The second electronic device may be separate from the first electronic device 150, or, in some cases, the first and second electronic devices may both be part of a same overall electronic device (e.g. components of a single device). In some examples, the first electronic device and the second electronic device are connected to one another in series.

[0031] The second control signal has either a third voltage for switching the second electronic device from a deactivated state to an activated state or a fourth voltage for switching the second electronic device from the activated state to the deactivated state. The third and fourth voltages define respective endpoints of a voltage range of the second control signal. In other words, the first control signal 120 has a voltage range defined by the first voltage and the second voltage, whereas the second control signal has a voltage range defined by the third voltage and the fourth voltage. The second level shifting circuit is configured to shift each endpoint of the voltage range of the second control signal by a second voltage offset to generate a second level shifted control signal. The second level shifting circuit is configured to output the second level shifted control signal to control the second electronic device.

[0032] The second voltage offset may be different than the first voltage offset. For example, the endpoints of the voltage range of the first control signal 120 may be shifted by 5V, whereas the endpoints of the voltage range of the second control signal may be shifted by 10V. Alternatively, the second voltage offset may be the same as the first voltage offset. As such, the endpoints of the voltage ranges of the first and second control signals may all be shifted by the same amount (e.g. 10V).

[0033] In some examples, the second voltage offset is dependent on the first level shifted control signal 130 generated by the first level shifting circuit 110. For example, the first level shifted control signal 130 may affect a node voltage at a node between the first device and the second device, and the second voltage offset may be determined based on the node voltage. This enables the second control signal to be adapted to dynamic conditions involving both devices. Alternatively, the second voltage offset may be independent of the first level shifted control signal 130.

[0034] The second voltage offset may be dependent on an operating condition of the first electronic device. Such an operating condition may comprise, for example, one or more of: whether the first electronic device is in the activated state or the deactivated state, an operating temperature of the first electronic device, an operating current of the first electronic device, etc. Additionally or alternatively, the second voltage offset may be dependent on an operating condition of the second electronic device. As such, the second voltage offset may be dependent on an operating condition of both the first electronic device and the second electronic device. Alternatively, the second voltage offset is independent of an operating condition of the first electronic device and / or the second electronic device.

[0035] The first level shifting circuit 110 and the second level shifting circuit may each comprise a respective plurality of logic inverters arranged in series. The plurality of logic inverters of the first level shifting circuit 110 may have the same characteristics (e.g. in terms of the number of logic inverters, the voltage offset applied by each logic inverter, the supply voltages received by each logic inverter, etc.) as the plurality of logic inverters of the second level shifting circuit, or alternatively the two pluralities of logic inverters may have one or more different characteristics from one another. Additionally or alternatively, the apparatus 100 may comprise one or more further level shifting circuits (e.g. a third level shifting circuit), comprising one or more further sets of logic inverters and operable to process control signals for one or more further electronic devices.

[0036] Figure 2 shows an example of a circuit 200 that may be controlled using the presently-disclosed methods. The circuit 200 is an example of an electronic device, such as the electronic device 150 described above. The circuit 200 comprises a driver circuit for light-emitting diodes 210, 220, 230, LEDs, in a series configuration between two reference voltages (a driving voltage, Vdd, and ground, or Vss). The LEDs 210, 220, 230 comprise a red, a green and a blue LED in this example. In this circuit, each LED 210, 220, 230 may be turned off by shorting, or bypassing, it with a transistor arranged in parallel with the LED. The transistor may be referred to as a 'bypass transistor’ or ‘bypass switch’. Turning a transistor off places a voltage across a respective LED sufficient to turn the LED on. Accordingly, the bypass transistors may be used to control the activation state of the LEDs 210, 220, 230. Additionally or alternatively, each LED (with corresponding bypass transistor) may be considered as an individual electronic device, such that the circuit 200 comprises three electronic devices connected in series.

[0037] In the example shown in Figure 2, a current sink for the LEDs is at 650 uA. It will be understood that the current sink (e.g. a circuit that ‘absorbs’ a specific amount of current) may have different values in other examples. A precision current sink may be implemented using a double cascode arrangement, for example. Additionally or alternatively, an external (off-chip) voltage reference may be used.

[0038] In the circuit 200 shown in Figure 2, it can be seen that the voltages at the nodes between LEDs 210, 220, 230 (nodes G, B and I) are variable, and may depend, for example, on the reference voltage Vdd, the on / off states of the other LEDs in the string, temperature, the precise current flowing throughout the circuit 200, etc. If the signal voltages (that is, the voltages of the control signals) for switching the bypass transistors on and off are referred to the ground (GND) reference, it may be difficult to apply the same gate-source voltage, e.g. 3V (depending on the characteristics of the transistor technology), to each transistor. It is therefore beneficial for the gate drive ‘on’ and ‘off’ voltages for each transistor to be referenced to that transistor’s source or drain voltage at the time the control signal is applied. For example, the ‘on’ voltage for the transistor bypassing the middle LED 220 may be made equal to the voltage at node G, and its ‘off’ voltage may be made equal to the voltage at node B, etc. In general, both the ‘on’ / ‘high’ level and the ‘off’ I ‘low’ level of each bypass transistor’s control voltage may be made responsive to the instant voltage at one or other of that transistor’s source or drain terminals. This may be achieved using the level shifting circuit 110 disclosed herein, which boosts (or shifts) the bypass transistor control signal voltages, in order to transform the standard control signal voltages (e.g. 0V and 3V) into more appropriate ranges for switching each of the bypass transistors.

[0039] In particular, the level shifting circuit 110 may generate dynamic bypass transistor control signals at incremental voltages, in steps of a transistor threshold voltage. This may be implemented as a series chain of logic inverters with rising supply (inverter Vdd and ground) voltages. An example of such an implementation is shown in Figure 3. The example level shifting circuit 110 shown in Figure 3 may be used to process control signals for electronic devices such as the three-LED series circuit 200 described above with reference to Figure 2. In particular, the example level shifting circuit 110 shown in Figure 3 may be used to control a bypass transister for the first, red, LED 210 in the circuit 200. The control signal 120 for a bypass transistor may be connected to the input of this chain, and the level-shifted output of the chain 130 may then be supplied to the gate of that bypass transistor, thereby to control the bypass transistor. Further level shifting circuits may be used to process bypass transistor control signals for the other LEDs 210, 230 in the circuit 200.

[0040] The level shifting circuit 110 shown in Figure 3 comprises four logic inverters 310, 320, 330, 340. However, it will be understood that the level shifting circuit 110 may comprise more or fewer logic inverters in other examples. In some cases, the logic shifting circuit 110 comprises only a single logic inverter. The dashed line in Figure 3 indicates the possible (optional) presence of further logic inverters between the third inverter 330 and the final inverter 340. For example, a greater number of voltage shift steps (and thus a greater number of inverters in the chain) may be used for devices and / or control signals that operate at higher voltages. The use of a chain of inverters with incrementally increasing supply voltages allows for incremental shifts in the voltage range of control signals. In particular, each logic inverter in the plurality of logic inverters 310, 320, 330, 340 may be configured to receive a different driving supply voltage and / or a different ground supply voltage. This enables the voltage range fo the control signal 120 to be incrementally shifted as it is processed by the chain of logic inverters. At least some of the driving and / or ground supply voltages for the logic inverters may correspond to the node voltages in the circuit 200, e.g. the I, R, G nodes, etc. Accordingly, the voltage offset(s) that are applied to the control signal 120 may vary with the node voltages (which may be dynamic, or time-varying). Some of the logic inverters may additionally or alternatively receive intermediate supply voltages, e.g. IS1, IS2, etc., rather than a supply voltage corresponding to a node voltage, e.g. G.

[0041] As mentioned above, a voltage mirror circuit may be used to supply one or more of the voltage offset(s) for the level shifting circuit 110. With reference to the LED driver circuit 200 shown in Figure 2, simply using the node voltages themselves to drive the bypass transistors could cause additional current loading of the G, B and I nodes or pins (R being at Vdd), and current drawn from these nodes could reduce the LED current. Therefore, it is beneficial to instead use a voltage mirror circuit to duplicate the node voltages and input the duplicate voltages into the level shifting circuit 110, rather than use the node voltages themselves.

[0042] In the voltage mirror circuit, the voltage at node G (as shown in Figure 2) may be duplicated to generate a duplicated voltage, Gbuf. If the voltage at node G increases, then a transistor connected directly to it may be more strongly turned on, so that it conducts more of the current sourced by the current sink from the reference voltage, Vdd. A diode-connected transistor in a parallel branch therefore conducts a lower share of this sink current, causing its source voltage (which is connected to Gbuf) to increase in proportion. Accordingly, an increase in the G voltage directly causes a corresponding increase in Gbuf, the duplicated voltage. The duplicated voltage Gbuf may then be used as an input to the level shifting circuit 110 (e.g. to affect the voltage offset to be applied to the control signal voltage range). Similar voltage mirror circuits may be used to replicate the voltages of the other variable nodes in the electronic device 200 (e.g. the nodes B, I). The voltage mirror circuit disclosed herein may be relatively compact and consumes modest current. Accuracy of duplication may also be sufficient for many applications, for example where a replicated voltage within approximately 100 mV of the node voltage is close enough to ensure successful operation. The response of the voltage mirror circuit may be made substantially linear and consistent over a large range of interest. Voltage mirrors may present no additional current load to the LED circuit, so the resulting LED current may be exactly that drawn by the current sink.

[0043] The node voltages may be duplicated in other ways, instead of a voltage mirror circuit, in other examples. For example, operational amplifiers may be used. This approach uses an operational amplifier to follow each node voltage, whilst presenting a high input impedance to the node. This may reproduce the node voltages more accurately than the voltage mirror approach described above.

[0044] In the level shifting circuit 110 shown in Figure 3, the supply voltages of the inverters in the level-shifting chain may be provided by a voltage supply circuit (not shown). This provides “intermediate levels” for device protection. An example of such a voltage supply circuit uses voltage dividers, e.g. a ladder of resistors between the circuit nodes to allow intermediate voltages to be tapped off. Another example of a voltage supply circuit for the level shifting circuit 110 uses voltage followers, e.g. using combinations of transistors and resistors to provide the in-between voltages.

[0045] The results of a simulation 400 of the level shifting circuit 110 applied to the LED driver circuit 200 are shown in Figure 4. In Figure 4, the upper four traces 410 in Figure 4 show the G, R, B and I node voltages over time. In the lower traces 420 in Figure 4, the level-shifted control voltages for each LED bypass transister track faithfully, at their boosted voltage ranges, the respective input control voltages. Further, these level-shifted control voltages track both the changing source and drain voltages (Vss and Vdd) of each bypass transistor.

[0046] This means that at the input of the level shifting circuit 110 the logic voltages (e.g. the transistor ‘off and ‘on’ voltages) may be, for example, 0V and 3V respectively, whilst at the output of the level shifting circuit 110 the transistor ‘off’ and ‘on’ voltages may be 12V and 15V, respectively. This is in contrast with some known circuits, in which the ground potential Vss (or the ‘off’ voltage) is fixed at 0V, even after level-shifting. In such known circuits, a 3V supply may be shifted to a 5V supply, for example, but the ground voltage does not (and / or cannot) change, and is fixed at zero. In some cases, the three-LED series circuit 200 shown in Figure 2 may require a voltage supply of Vdd « 10-15V. That is, the driver circuit 200 may be a high voltage circuit. A transistor connected to Vdd of 15V would therefore need to be able to withstand at least 15V within that transistor, because its bulk terminal would still be at 0V (in some known systems). Such a voltage may exceed the maximum rated value for the transistor. This could damage the transistor and / or affect the transistor characteristics. Accordingly, such a driver circuit may be difficult to implement and / or control using known methods. Unlike such known methods, both endpoints of the voltage range of the control signal are shifted by the presently-disclosed level shifting circuit 110. Thus the requirements on transistor devices in terms of voltages to be withstood within the transistor may be reduced.

[0047] Figure 5 shows a flow chart illustrating the steps of a method 200 of processing control signals using a level shifting circuit, according to the present disclosure. The method 500 may be performed at least in part by the apparatus 100 described above with reference to Figure 1, and in particular by the level shifting circuit 110 of the apparatus 100.

[0048] A first step of the method 500, illustrated by item 510, comprises receiving a control signal. The control signal is operable to control an electronic device, such as the electronic device 150 described above. The control signal has either a first voltage, for switching the electronic device from a deactivated state to an activated state, or a second voltage, for switching the electronic device from the activated state to the deactivated state. The control signal is switchable between the first voltage and the second voltage in order to control the electronic device. That is, the control signal may have the first voltage at some times and the second voltage at other times. In other words, the control signal takes both values (the value of the first voltage and the value of the second voltage), but not at the same time. The first voltage and the second voltage define respective endpoints of a voltage range of the control signal.

[0049] A second step, illustrated by item 520, of the method 500 comprises shifting each endpoint of the voltage range of the control signal by a voltage offset to generate a level shifted control signal. This may involve, for example, processing the control signal using one or more logic inverters, as described above.

[0050] A third step, illustrated by item 530, of the method 500 comprises outputting the level shifted control signal to control the electronic device. For example, the level shifted control signal may cause the electronic device to be activated or deactivated.

[0051] Figure 6 shows schematically circuitry 600 comprising a plurality of logic inverters 610, 620, 630 connected in series. The circuitry 600 is an example of a level shifting circuit such as the level shifting circuit 110 described above. Each of the plurality of logic inverters 610, 620, 630 is arranged to receive a different supply voltage.

[0052] The circuitry 600 is configured to receive a control signal 640 operable to control an electronic device. The control signal 640 has either a first voltage for switching the electronic device from a deactivated state to an activated state, or a second voltage for switching the electronic device from the activated state to the deactivated state. The control signal 640 is switchable between the first and the second voltage to control the electronic device. The first voltage and the second voltage define respective endpoints of a voltage range of the control signal 640.

[0053] The circuitry 600 is configured to process the control signal 640 using at least one logic inverter of the plurality of logic inverters 610, 620, 630 to generate a level shifted control signal 650. Each of the plurality of logic inverters 610, 620, 630 is configured to offset each endpoint of the voltage range of the control signal 640 by a given voltage. The control signal 640 may be processed by one, some, or all of the logic inverters 610, 620, 630.

[0054] The circuitry 600 is configured to output the level shifted control signal 350 to control the electronic device.

[0055] Whilst the present disclosure has been described and illustrated with reference to particular embodiments or examples, it will be appreciated by those of ordinary skill in the art that the disclosure lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0056] The level shifting circuit 110 may be configured to apply a positive voltage offset to the endpoints of the voltage range of the control signal 120. That is, the level shifted control signal 130 may have a higher voltage range than the initial control signal 120. Additionally or alternatively, the level shifting circuit 110 may be configured to apply a negative voltage offset to the endpoints of the voltage range of the control signal 120. That is, the level shifted control signal 130 may have a lower voltage range than the initial control signal 120 in some cases.

[0057] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the disclosure, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. Apparatus comprising a level shifting circuit configured to:receive a control signal operable to control an electronic device, the control signal having either a first voltage for switching the electronic device from a deactivated state to an activated state or a second voltage for switching the electronic device from the activated state to the deactivated state, the first voltage and the second voltage defining respective endpoints of a voltage range of the control signal;shift each endpoint of the voltage range of the control signal by a voltage offset to generate a level shifted control signal; andoutput the level shifted control signal to control the electronic device.

2. Apparatus according to claim 1, wherein the level shifting circuit comprises one or more logic inverters.

3. Apparatus according to any preceding claim, wherein the level shifting circuit comprises a plurality of logic inverters connected in series.

4. Apparatus according to claim 3, wherein each logic inverter in the plurality of logic inverters is configured to receive a different supply voltage.

5. Apparatus according to claim 3 or claim 4,wherein each logic inverter in the plurality of logic inverters is configured to receive a respective driving supply voltage and a respective ground supply voltage, andwherein each logic inverter in the plurality of logic inverters is configured to receive a different ground supply voltage.

6. Apparatus according to any preceding claim, wherein the voltage offset is dependent on an operating condition of the electronic device.

7. Apparatus according to claim 6, wherein the operating condition comprises one or more of: whether the electronic device is in the activated stateor the deactivated state, an operating temperature of the electronic device, an operating current of the electronic device, or an operating state of a further electronic device.

8. Apparatus according to any preceding claim, wherein the voltage offset is dependent on a source voltage and / or a drain voltage of the electronic device.

9. Apparatus according to any preceding claim, wherein one of the first voltage and the second voltage is zero volts.

10. Apparatus according to any preceding claim, wherein the electronic device comprises a transistor.

11. Apparatus according to any preceding claim, wherein the electronic device comprises a light emitting diode, LED.

12. Apparatus according to claim 11, wherein the control signal is operable to change a state of a bypass transistor connected in parallel with the LED.

13. Apparatus according to claim 12, wherein outputting the level shifted control signal comprises outputting the level shifted control signal to a gate of the bypass transistor.

14. Apparatus according to any preceding claim, wherein the electronic device comprises a plurality of LEDs connected in series.

15. Apparatus according to claim 14, wherein the voltage offset is dependent on a voltage at a common connection of a first LED of the plurality of LEDs and a second LED of the plurality of LEDs.

16. Apparatus according to any preceding claim, wherein the apparatus comprises the electronic device.

17. Apparatus according to any preceding claim, wherein the voltage offset is the same for each endpoint of the voltage range of the control signal.

18. Apparatus according to any preceding claim, wherein the apparatus comprises or is comprised on an integrated circuit formed from thin films on an insulating substrate.

19. Apparatus according to any preceding claim, wherein the apparatus comprises or is comprised on a flexible integrated circuit.

20. Apparatus according to any preceding claim, wherein the apparatus is configured to receive the voltage offset from a voltage mirror circuit.

21. Apparatus according to claim 20, wherein the voltage mirror circuit is configured to duplicate a source voltage and / or a drain voltage of the electronic device.

22. Apparatus according to claim 20 or claim 21, wherein the apparatus comprises the voltage mirror circuit.

23. Apparatus according to any preceding claim,wherein the level shifting circuit is a first level shifting circuit, the voltage offset is a first voltage offset, the level shifted control signal is a first level shifted control signal, and the electronic device is a first electronic device, andwherein the apparatus comprises a second level shifting circuit configured to:receive a second control signal operable to control a second electronic device, the second control signal having either a third voltage for switching the second electronic device from a deactivated state to an activated state or a fourth voltage for switching the second electronic device from the activated state to the deactivated state, the third voltage and the fourth voltage defining respective endpoints of a voltage range of the second control signal;shift each endpoint of the voltage range of the second control signal by a second voltage offset to generate a second level shifted control signal; andoutput the second level shifted control signal to control the second electronic device.

24. Apparatus according to claim 23, wherein the second voltage offset is dependent on the first level shifted control signal generated by the first level shifting circuit.

25. Apparatus according to claim 23 or claim 24, wherein the second voltage offset is different than the first voltage offset.

26. Apparatus according to any of claims 23 to 25, wherein the second voltage offset is dependent on an operating condition of the first electronic device.

27. A method of processing control signals using a level shifting circuit, themethod comprising, at the level shifting circuit:receiving a control signal operable to control an electronic device, the control signal having either a first voltage for switching the electronic device from a deactivated state to an activated state or a second voltage for switching the electronic device from the activated state to the deactivated state, the first voltage and the second voltage defining respective endpoints of a voltage range of the control signal;shifting each endpoint of the voltage range of the control signal by a voltage offset to generate a level shifted control signal; andoutputting the level shifted control signal to control the electronic device.

28. Circuitry comprising a plurality of logic inverters connected in series, each of the plurality of logic inverters being arranged to receive a different supply voltage, the circuitry being configured to:receive a control signal operable to control an electronic device, the control signal having either a first voltage for switching the electronic device from a deactivated state to an activated state or a second voltage for switching the electronic device from the activated state to the deactivated state, the firstvoltage and the second voltage defining respective endpoints of a voltage range of the control signal;process the control signal using at least one logic inverter of the plurality of logic inverters to generate a level shifted control signal, each of the plurality5 of logic inverters being configured to offset each endpoint of the voltage range of the control signal by a given voltage; andoutput the level shifted control signal to control the electronic device.

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