Current controlled current source, and methods of controlling a current source and/or regulating a circuit

Current sources, systems including the current source, and methods for regulating and/or controlling a circuit using the current source. The current source is generally configured to (i) receive a reference current, a bias voltage and a feedback/input current and (ii) provide an output current. The systems generally include the current source, a circuit directly or indirectly receiving the output current, a bias source/generator configured to provide the bias voltage, and a current reference configured to sink or source a predetermined amount of current from or to the output current. The method generally includes (a) applying a bias voltage to the current source, the current source receiving an input current and providing an output current; (b) sinking or sourcing a reference current from or to the output current; (c) applying the output of the current source directly or indirectly to a regulated circuit; and (d) providing the input current from the regulated circuit.

FIELD OF THE INVENTION

The present invention generally relates to the field of analog integrated circuit designs. More specifically, embodiments of the present invention pertain to current sources and methods for regulating and/or controlling a circuit using a current source.

DISCUSSION OF THE BACKGROUND

A feedback loop in a conventional regulator system typically uses voltage feedback and a resistive voltage divider to set the regulated output voltage relative to an input reference voltage. The difference of these two signals (i.e., the regulated output voltage and the reference voltage) is usually obtained by standard connections in an operational amplifier (“op amp”), differential amplifier, or transconductance amplifier, which operate on the voltage signals.

FIG. 1shows a conventional op amp- or differential amp-based voltage regulator10. A voltage divider30(comprising first and second resistors32and34in series between a regulated voltage VOUTand a ground potential36) provides a first input into the op amp/differential amp20. A conventional bias source40(e.g., a conventional bias voltage generator) provides a second input (i.e., a reference voltage VREF) into the op amp/differential amp20. The difference ΔV between the two input signals is output to the signal path having a node at which the voltage (VOUT) is regulated, thereby providing a feedback path to the voltage-controlled voltage source10.

In the example shown inFIG. 1, the ground potential36in the voltage divider30is a system potential, whereas the ground potential42for the voltage source40is a reference ground. The different ground potentials may have different values due to different noise effects (e.g., from the system vs. on the chip). As a result, when the feedback loop is closed, the regulated voltage VOUThas a value that can be defined according to the following Equation (1):
VOUT=(VREF±ΔGND)(1+(R2/R1))  (1)
where ΔGND is the voltage difference between the different ground potentials36and42, R1 is the resistance of resistor32, and R2 is the resistance of resistor34.

In such a system, the sensitivity of the regulated voltage VOUTto ground noise is:
dVOUT/dΔGND=R2/R1  (3)

In many systems, it is difficult to maintain a solid ground reference between the output voltage and reference voltage. For example, in a white LED (WLED) backlighting system, the DC ground reference for the output voltage in a boost regulator IC is external to the IC, whereas the voltage reference signal is internal. This creates noise susceptibility and, in a high power system, erratic regulator behavior, particularly if the ratio of the output voltage to the reference voltage is large. In many boost converter applications, the output voltage to reference voltage ratio can be as high as 40:1. This means a ground noise level of 100 mV shows up on the regulated output multiplied by 40× (i.e., 4V).

FIG. 2shows a voltage-controlled transconductance control circuit10′. When the input VOUTis part of a feedback loop from a node in the signal path being controlled, the control circuit10′ and the feedback loop together may be considered to be a regulator. The transconductance control circuit10′ includes a transconductance amplifier20′, and operates similarly to the op amp-based regulator10ofFIG. 1, except that the output current ΔI from the transconductance amplifier20′ controls or biases a current source50, which outputs a current IOUThaving a value equal to the gain of the transconductance amplifier20′ times the voltage VFBfrom the voltage divider30. However, the value of voltage VOUTis still defined according to Equation (1) above. As a result, variations in the different ground potentials can cause significant variations in the regulated current output from the transconductance control circuit10′.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate to circuits and methods for regulating and/or controlling a circuit using a current source. In one aspect (e.g., “closed loop” embodiments), the circuit generally includes a current source configured to receive a reference current, a bias voltage and a feedback current, the current source providing an output current; a regulated circuit, directly or indirectly receiving the output current and directly or indirectly providing the feedback current; and a current reference, configured to sink a predetermined amount of current from the output current or source a predetermined amount of current to the output current. The method generally includes (a) applying a bias voltage to the current source, the current source receiving an input current and providing an output current; (b) sinking or sourcing a reference current from or to the output current, wherein the output current represents a difference between the input current and the reference current; and (c) applying the output current directly or indirectly to a regulated circuit.

Another aspect of the invention involves a circuit that includes a bias source and/or generator configured to provide a bias voltage; a current reference configured to sink or source a predetermined amount of current; and a current source (e.g., a current-controlled current source) configured to receive the predetermined amount of current, the bias voltage and an input current, the current source providing an output current representing a difference between the input current and the predetermined amount of current. In some embodiments, the current source includes a transistor having a first terminal receiving the input current, a second terminal providing the output current, and a control terminal receiving the bias voltage.

Yet another aspect of the invention (e.g., “open loop” embodiments) involves a circuit that includes a current controlled current source configured to receive a bias voltage and an input current, the current controlled current source providing an output current; a circuit configured to receive the output current; a bias source and/or generator configured to provide the bias voltage; and a current reference, configured to sink or source a predetermined amount of current from or to the output current. In various embodiments, the circuit configured to receive the output current can include a filter, integrator and/or current-to-voltage converter that controls a predetermined voltage to a regulated circuit; a detector circuit configured to detect an excursion in another circuit; or an enable circuit configured to enable another circuit in response to the output current meeting one or more predetermined criteria.

The problem inFIGS. 1-2relating to reference voltages to different ground potentials can be solved by first converting the regulated voltage and the reference voltage to current signals, and then operating (e.g., performing a linear operation, such as subtraction or addition, and then optionally performing a scaling operation) on the current signals using a current controlled current source, which in various embodiments can be as simple as a single common bipolar transistor or MOS field effect transistor (FET). Now, the output voltage to current conversion takes place with an effective voltage ratio of 1:1, and thus, the noise immunity is improved by 40×. Additional benefits of the present invention include a very small transconductance gain (e.g., it is relatively easy to obtain 33 nmhos using widely available CMOS and analog semiconductor manufacturing technologies), an intrinsic current comparator function, and a naturally high output impedance that can directly drive loop filter and additional control functions. These and other advantages of the present invention will become readily apparent from the detailed description of preferred embodiments below.

DETAILED DESCRIPTION

For the sake of convenience and simplicity, the terms “connected to,” “coupled with,” “coupled to,” and “in communication with,” are generally used interchangeably herein, but are generally given their art-recognized meanings.

The present invention concerns a circuit and method for controlling a current source. The circuit generally includes a current source configured to receive a reference current, a bias voltage and a feedback current, the current source providing an output current; a regulated circuit, directly or indirectly receiving the output current and directly or indirectly providing the feedback current; and a current reference, configured to sink or source a predetermined amount of current from or to the output current. The method generally includes (a) applying a bias voltage to the current source, the current source receiving a feedback current and providing an output current; (b) sinking or sourcing a reference current from or to the output current; (c) applying the output of the current source to a regulated circuit; and (d) providing the feedback current from the regulated circuit.

The invention, in its various aspects, will be explained in greater detail below with regard to exemplary embodiments.

Exemplary Regulated Systems Using a Current-Controlled Current Source

FIG. 3shows a first exemplary system100employing a current-controlled current source110and a circuit170having a voltage that is regulated by the current-controlled current source110. The current-controlled current source110receives a feedback current IFBfrom the regulated circuit170(through a feedback resistor130), a reference current from a current source140, and a bias voltage from a bias source/generator150. Generally, the bias voltage from the bias source/generator150biases the current-controlled current source110. Also, the feedback “resistor”130may simply represent a resistance of a feedback path and/or of a circuit in the feedback path from the regulated circuit170to the current-controlled current source110.

Thus, aspects of the current-controlled current source110relate to a circuit including a bias source and/or generator150, a current reference140and a current source112. The bias source and/or generator150is generally configured to provide a bias voltage (e.g., VBIAS). The current reference140is generally configured to sink or source a predetermined amount of current (e.g., IREF, which can be positive or negative). The current source112generally receives IREF, the bias voltage and an input current (e.g., IFB), and provides an output current (e.g., directly at115, or indirectly, IOUT). In various embodiments, the current source112is controlled by the bias voltage VBIAS.

An output115of the current-controlled current source110is a current signal that represents the difference between the feedback current IFBand the reference current (IREF) from the current source140. The current signal115from the current-controlled current source110may control a second current source120, which provides an output current IOUTthat is converted to a voltage by the filter and/or integrator160. In such a configuration, the second current source120may also receive an input current (not shown) from a conventional current source or a power rail (e.g., VCC or ground), either directly (generally in the case of a current source) or through a resistor (generally in the case of a power rail; also not shown). Alternatively, the current signal115may be input directly into the filter/integrator160or amplified by a known current amplification circuit.

The output current IOUThas a value equal to AI·(IFB−IREF), where AIis the gain of the second current source120or any current amplifier receiving the output115of the current-controlled current source110. The filter/integrator160then outputs a voltage that is applied to the regulated circuit170. Thus, the filter/integrator160can either include or be replaced with a current-to-voltage converter. The voltage from the filter/integrator160controls a voltage regulated in the regulated circuit170, and as a result, can adjust itself to keep the output OUT in regulation.

The regulated circuit170can be any circuit (analog, digital, or mixed signal) that can use a feedback control system. In one example, the regulated circuit170is a switching regulator, a boost regulator, or a buck regulator. In other examples, the regulated circuit170can be an op amp, a pulse width modulator, a timing generator (e.g., a clock generator, such as a phase-locked loop or a voltage-controlled oscillator, or other periodic signal generator), a power amplifier (e.g., in a relatively high power/high voltage system, where the voltages generally are greater than or equal to 20V, 40V, or more), or a switch and/or driver for an LED lighting system, a display, an audio system, or a power conversion system. It is within the abilities of one skilled in the art to design such regulated circuits and use the present current controlled current source to regulate and/or control such regulated circuits. An output (e.g., OUT) of the regulated circuit170is fed back (through resistor130) to the current-controlled current source110for comparison with the reference current from current source140.

Similar to the systems ofFIGS. 1-2, the bias source/generator150can be coupled to a system ground potential152(e.g., external to the IC), whereas the current source140can be coupled to a reference potential142(e.g., internal to the IC). The voltage (VOUT) of the signal output by the regulated circuit170has a value defined by the following Equation (4):
VOUT=(IFB·R)+VBIAS+ΔGND(4)
where R is the resistance of resistor130and Vbiasis the bias voltage from the bias source/generator150.

When the ground potential152connected to the bias source/generator150is a system (or external) ground potential, ΔGND≠0, and dVOUT/dΔGND=1. Alternatively, when the ground potential152connected to the bias source/generator150is a reference (or internal) ground potential, dVOUT/dΔGND=0, and the variation in the voltage applied to the regulated circuit170is independent of the gain of the regulator (i.e., the current-controlled current source feedback loop).

In an alternative embodiment, the ground potential142connected to the bias source/generator140can be a system ground potential, which can result in a dVOUT/dΔGND=0, but such a configuration generally requires an extra or dedicated pin to connect the reference current generator140to a system ground potential. Because the reference current IREFis provided by the current source generator140, the value of the ground potential142with respect to any other ground potential (e.g., ground potential152) is irrelevant. However, the bias voltage source150generally requires connection to a ground potential (e.g., ground potential152), which can either be an internal ground or external (system) ground. When the ground potential152is an internal ground, the sensitivity of the current-controlled current source110equals 1, and when the ground potential152is an external ground, the sensitivity of the current-controlled current source110equals 0 (when system ground is defined as the reference ground). Thus, the effect of ground noise and/or differences between different ground potentials in feedback-regulated voltages can be made independent of the gain of the system100.

FIG. 4shows a second exemplary system100′ employing the current-controlled current source110and a plurality of circuits170,172,174each having a voltage that is regulated by the present current-controlled current source110. The current-controlled current source110is substantially the same as the current-controlled current source110ofFIG. 3. However, the output115of current-controlled current source110can control multiple current sources122,124,126, respectively providing a regulated current to a filter/integrator160, a detector172and an enable circuit174. Similarly to the embodiment shown inFIG. 3, the filter/integrator160provides a regulated voltage to the regulated circuit170, which in turn provides a feedback signal to the current-controlled current source110. Thus, the filter/integrator160and the regulated circuit170are part of a closed loop circuit.

As shown inFIG. 4, current sources124and126are in parallel with each other and with current source122and filter/integrator160. Each of the detector172and enable circuit174receive a regulated current from the corresponding current sources124and126, respectively, and can be part of an open loop circuit. Such “open loop” circuits generally include a current controlled current source (e.g.,110) configured to receive a bias voltage VBIASand an input current (e.g., IFB), a circuit configured to receive the output current115from the current controlled current source110, a bias source and/or generator configured to provide the bias voltage VBIAS; and a current reference configured to sink or source a predetermined amount of current (e.g., IREF) from or to the output current. The detector172and enable circuit174may take advantage of the intrinsic current comparator function provided by the present current-controlled current source110.

For example, the detector172can be configured to detect an excursion (e.g., in the regulated circuit170or elsewhere on the chip or in the system) above or below the regulated current at node125(or above or below a predetermined difference between the regulated current at node125and a reference current), and activate a control signal173that notifies the user of the excursion and/or that turns on, turns off, resets or adjusts (e.g., change an operational mode of) one or more circuits elsewhere on the chip or in the system. Alternatively, the current signal125can be converted to a voltage (e.g., using an analog-to-digital converter or a filter/integrator similar to filter/integrator160), and the detector172can detect an excursion in such a voltage or voltage difference. In further embodiments, there can be more than one detector receiving the output115from the current-controlled current source110.

Similarly, the enable circuit174can provide an active enable signal175enabling (e.g., turning on or activating) one or more circuits elsewhere on the chip or in the system in response to the regulated current at node127meeting one or more predetermined criteria (e.g., being above a first current value and/or below a second current value). Alternatively, the current signal127can be converted to a voltage similarly to the current signal125, and the enable circuit174can provide an active enable signal175in response to the voltage meeting one or more predetermined criteria (e.g., being above a first voltage and/or below a second voltage). Thus, as a result of the intrinsic current comparator function provided by the current-controlled current source110, functionality in addition to current/voltage regulation can be enabled on the chip and/or in the system.

More specifically, in various embodiments, a linear control loop including the filter/integrator160and the regulated circuit170can be controlled by the current-controlled current source110in a closed loop control system (e.g., the system100inFIG. 3). An open control loop including the current-controlled current source110and the detector172has at least two functions. The first function monitors the state of the current-controlled current source110and determines if the loop is within a regulation window (e.g., whether the loop has reached a steady state condition of regulation). In this case, the detector172may serve as a comparator with a predetermined margin (e.g., ±2%, ±5%, ±100 μOhms, ±0.1V, etc.) around a steady state target parameter value. So, the detector172(and the enable circuit174) can operate in an open loop manner and generate a logic signal (e.g., output signal173,175).

However, the additional function blocks (e.g., the detector172and/or the enable circuit174) can also operate in a non-linear closed loop control mode (e.g., using pulse frequency modulation [PFM]), whereby the linear loop path is open after the current source124or126(or, when present, an integrator receiving the output of the current source124or126). The detector172or enable circuit174continues to monitor the state of the current-controlled current source110, but the logic signal output by the detector172or enable circuit174controls the regulator loop (e.g., in a “bang-bang” fashion) around the regulation window (e.g., the predetermined margin).

The system100′ can improve the power efficiency of the system100and/or a chip containing the system100(FIG. 3), because the additional functions (e.g., detector172and/or enable circuit174inFIG. 4) require only a simple additional current reference source (e.g., current source124or126) for each function. Additional comparators are not needed for the additional function blocks. As a result, capacitive loading on the feedback input IFBis reduced because the additional comparators that would normally be connected to this node for monitoring (e.g., similar to the current-controlled current source110) are not present. Thus, the current controlled current source110can provide benefits to the system100for battery-powered applications (e.g., LED flashlights, mobile displays, etc.).

In fact, the additional functions shown inFIG. 4can also be provided in a voltage-controlled current source (e.g., a transconductance amplifier-based system such as that shown inFIG. 2) by providing only an additional current source per detector function at the output of the transconductance amplifier, thereby reducing total area and power relative to a system that uses a separate transconductance amplifier for each function. Thus, in one embodiment, a transconductance amplifier can replace the current-controlled current source (CCCS)110in the system100′.

Exemplary Current-Controlled Current Sources

In another aspect, the present invention relates to a current-controlled current source that includes, for example, a transistor configured to output a difference between a feedback current and a reference current, such as the exemplary circuit200ofFIG. 5A. In various embodiments, the current controlled current source includes a transistor having a first terminal receiving the feedback (or input) current, a second terminal providing the output current, and a control terminal receiving a bias voltage.

The exemplary circuit200ofFIG. 5Aincludes a PMOS transistor212, a resistor230, and a reference current source240. A feedback current IFBis provided from the feedback voltage VOUTof the regulated circuit (not shown) across the resistor230. The reference current source240provides a reference current IREFto or from an output node215of the current-controlled current source. The PMOS transistor212receives a bias voltage VBIASat its gate, and is thus configured to output a current at node215that represents a difference between IFBand IREF. The bias voltage VBIAScan be the bias voltage provided by the exemplary bias source/generator150ofFIG. 3.

In the embodiment shown inFIG. 5A, the current output signal215is received directly at a loop filter or integrator260. The loop filter/integrator260includes first and second capacitors262and264and resistor263. As shown inFIG. 5A, the first capacitor262and the resistor263are in series between a node215and a ground potential (e.g., reference ground265), and the second capacitor264is in parallel with the first capacitor262and the resistor263. The loop filter/integrator260is configured to store charge from the current output signal215, convert the current output signal215to a voltage signal within a particular time domain (e.g., of the system100inFIG. 3, in which the regulated circuit may provide an output having a periodic waveform, such as a square wave or a sawtooth/triangular wave having a duty cycle, e.g., of from 40-60%), and/or drive the current difference at node215(e.g., IFB−IREF) to zero.

In a further embodiment (e.g., similar to the system100ofFIG. 3), a variable current source can be placed between the output node215and the loop filter260. In an alternative embodiment, the loop filter260can be placed between the transistor212and a variable current source (e.g.,120inFIG. 3). Also, the loop filter/integrator260can be replaced with a linear regulator or an RL filter (e.g., comprising a resistor and an inductor, each receiving the output current at node215) configured to maintain the output current in the current domain before further processing by downstream circuitry (e.g., the detector172and/or enable circuit174inFIG. 4).

A further embodiment of the present current-controlled current source is shown inFIG. 5B. The current-controlled current source200′ is essentially a complementary version of the current-controlled current source200ofFIG. 5A. The current-controlled current source200′ ofFIG. 5Bincludes an NMOS transistor214, a resistor232, and a reference current source242. The feedback current IFBis sunk by the feedback voltage VOUTof the regulated circuit (not shown), across the resistor232. The reference current source240sources a reference current IREFfrom an upper power supply VCC. The NMOS transistor214receives a bias voltage VBIAS′ at its gate, similar (but complementary) to the bias voltage VBIASat the gate of PMOS transistor212(FIG. 5A). The NMOS transistor214(FIG. 5B) is thus configured to output a current at node215that represents a difference between IFBand IREF(e.g., IREF−IFB).

The current output signal217is received directly at a loop filter or integrator260similar to the loop filter/integrator260ofFIG. 5A. In further embodiments, a variable current source can be placed between the output node217and the loop filter260, and the loop filter/integrator260can be replaced with a linear regulator.

A still further embodiment of the present current-controlled current source is shown inFIG. 5C. The current-controlled current source200″ ofFIG. 5Cincludes an NPN bipolar junction transistor216, a resistor230, and a reference current source240. The resistor230and reference current source240can be substantially the same as those shown inFIG. 5A. In the current-controlled current source200″ ofFIG. 5C, the feedback current IFBis provided from the feedback voltage VOUTof the regulated circuit (not shown) across the resistor230. The reference current source240sinks a reference current IREFfrom an output node215of the current-controlled current source. The NPN bipolar junction transistor216receives a bias voltage VBIASat its base, and is thus configured to output a current at node219that represents a difference between IFBand IREF(e.g., IFB−IREF). The bias voltage VBIAScan be the bias voltage provided by the exemplary bias source/generator150ofFIG. 3. The current-controlled current source200″ ofFIG. 5Coutputs a current difference signal219that is generally not affected by a threshold voltage of the transistor and that has a gain that may have a larger linear range as a function of the bias voltage VBIASand/or the difference between IFBand IREF.

Like the current-controlled current sources200and200′ ofFIGS. 5A-B, the current output signal219from the current-controlled current source200″ ofFIG. 5Cis received directly at a loop filter or integrator260, and in further embodiments, a variable current source can be placed between the output node217and the loop filter260, and/or the loop filter/integrator260can be replaced with a linear regulator.

An Exemplary Method

The present invention further relates to method of regulating or controlling a current and/or voltage in a circuit using a current-controlled current source. In general, a bias voltage is applied to the current-controlled current source, and a reference current is sunk from or sourced to the current output by the current-controlled current source. The output current generally represents a difference between a current input to the current-controlled current source and the reference current. The output current is then applied directly or indirectly to a regulated circuit. A flow chart300for an exemplary method of regulating or controlling a current and/or voltage in a circuit is shown inFIG. 6.

At310, and as discussed above, the current-controlled current source (CCCS) receives a feedback current (IFB), a reference current (IREF) and a bias voltage (VBIAS). In various embodiments, and as a discussed above (e.g., with regard toFIGS. 5A-5C), the CCCS can include a transistor configured to receive the feedback current from the circuit regulated by the present method at a first terminal (e.g., a source or drain) of the transistor and the reference current at a second terminal (e.g., the other of the source or drain) of the transistor. As shown in320ofFIG. 6, the bias voltage is applied to the CCCS, generally at the gate or base of the transistor in transistor-based embodiments. Typically, the feedback current is generated by applying a feedback voltage from the regulated circuit to an input of a feedback resistor coupled to the first terminal of the transistor. The reference current can be generated by a conventional fixed current source, and the bias voltage can be generated by a conventional fixed bias or voltage generator. Appropriate values of the reference current and the bias voltage can be determined by those skilled in the art without undue experimentation.

As a result, at330, the current difference IFB−IREFis output from the CCCS to a filter/integrator. The current difference IFB−IREFis generally a regulated current, which can be used for various purposes as a result of the intrinsic current comparator function provided by the CCCS. For example, the regulated current can be used to detect an excursion in the regulated circuit (or elsewhere on the chip or in the system) above or below the regulated current (or a regulated voltage corresponding thereto). Also, the regulated current can be used to enable or activate one or more circuits elsewhere on the chip or in the system in response to the regulated current meeting one or more predetermined criteria. In various embodiments, the filter/integrator is the same as or similar to loop filter260inFIG. 5A.

As discussed elsewhere herein, the filter/integrator converts the current difference IFB−IREFto a (regulated) voltage, and at340, the (regulated) voltage is output from the filter/integrator to the regulated (or voltage-controlled) circuit. As described elsewhere herein, the regulated circuit can be any circuit that uses a feedback control system, such as a switching regulator, an op amp, a pulse width modulator, a timing generator or other periodic signal generator, a power amplifier, a switch and/or driver for an LED or other lighting or display system, an audio system, or a power conversion system.

At360, an output of the regulated circuit is then fed back to the CCCS. In various embodiments, an output voltage is fed through a resistor (or other voltage-to-current converter) to generate a feedback current (e.g., IFB). The feedback current is then received by the CCCS at310, thereby completing the loop.

The present invention provides circuits and methods for controlling a current source. In one aspect (e.g., “closed loop” embodiments), the circuit generally includes a current source configured to receive a reference current, a bias voltage and a feedback current, the current source providing an output current; a regulated circuit, directly or indirectly receiving the output current and directly or indirectly providing the feedback current; and a current reference, configured to sink or source a predetermined amount of current from or to the output current. Another aspect of the invention involves a circuit (e.g., for implementing a current-controlled current source) that includes a bias source and/or generator configured to provide a bias voltage; a current reference configured to sink or source a predetermined amount of current; and a current source configured to receive the predetermined amount of current, the bias voltage and an input current, the current source providing an output current representing a difference between the input current and the predetermined amount of current. Yet another aspect of the invention (e.g., “open loop” embodiments) involves a circuit that includes a current controlled current source configured to receive a bias voltage and an input current, the current controlled current source providing an output current; a circuit configured to receive the output current; a bias source and/or generator configured to provide the bias voltage; and a current reference, configured to sink or source a predetermined amount of current from or to the output current. The method generally includes (a) applying a bias voltage to the current source, the current source receiving an input current and providing an output current; (b) sinking or sourcing a reference current from or to the output current, the output current representing a difference between an input current to the current source and the reference current; and (c) applying the output current to a regulated circuit.