Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
  • G05F3/02—Regulating voltage or current
  • G05F3/08—Regulating voltage or current wherein the variable is DC
  • G05F3/10—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics
  • G05F3/16—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices
  • G05F3/20—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
  • G05F3/26—Current mirrors
  • G05F3/265—Current mirrors using bipolar transistors only
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
  • G05F3/02—Regulating voltage or current
  • G05F3/08—Regulating voltage or current wherein the variable is DC
  • G05F3/10—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics
  • G05F3/16—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices
  • G05F3/20—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
  • G05F3/22—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only
  • G05F3/222—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only with compensation for device parameters, e.g. Early effect, gain, manufacturing process, or external variations, e.g. temperature, loading, supply voltage
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
  • G05F3/02—Regulating voltage or current
  • G05F3/08—Regulating voltage or current wherein the variable is DC
  • G05F3/10—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics
  • G05F3/16—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices
  • G05F3/20—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
  • G05F3/22—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only
  • G05F3/222—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only with compensation for device parameters, e.g. Early effect, gain, manufacturing process, or external variations, e.g. temperature, loading, supply voltage
  • G05F3/225—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations wherein the transistors are of the bipolar type only with compensation for device parameters, e.g. Early effect, gain, manufacturing process, or external variations, e.g. temperature, loading, supply voltage producing a current or voltage as a predetermined function of the temperature
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
  • G05F3/02—Regulating voltage or current
  • G05F3/08—Regulating voltage or current wherein the variable is DC
  • G05F3/10—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics
  • G05F3/16—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices
  • G05F3/20—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
  • G05F3/30—Regulators using the difference between the base-emitter voltages of two bipolar transistors operating at different current densities
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/45—Differential amplifiers
  • H03F3/45071—Differential amplifiers with semiconductor devices only
  • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
  • H03F3/45179—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using MOSFET transistors as the active amplifying circuit
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/45—Differential amplifiers
  • H03F3/45071—Differential amplifiers with semiconductor devices only
  • H03F3/45076—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier
  • H03F3/45475—Differential amplifiers with semiconductor devices only characterised by the way of implementation of the active amplifying circuit in the differential amplifier using IC blocks as the active amplifying circuit
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/45—Differential amplifiers
  • H03F3/45071—Differential amplifiers with semiconductor devices only
  • H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
  • H03F3/45928—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection using IC blocks as the active amplifying circuit
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2200/00—Indexing scheme relating to amplifiers
  • H03F2200/447—Indexing scheme relating to amplifiers the amplifier being protected to temperature influence
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2200/00—Indexing scheme relating to amplifiers
  • H03F2200/456—A scaled replica of a transistor being present in an amplifier
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F2203/00—Indexing scheme relating to amplifiers with only discharge tubes or only semiconductor devices as amplifying elements covered by H03F3/00
  • H03F2203/45—Indexing scheme relating to differential amplifiers
  • H03F2203/45564—Indexing scheme relating to differential amplifiers the IC comprising one or more extra current sources

Definitions

• Bandgap reference voltage supplies are used in various electronic applications. These voltage supplies provide constant reference voltages despite power supply variations, load variations, and temperature changes.
• a bandgap reference circuit includes first through fourth bipolar junction transistors (BJTs).
• BJTs bipolar junction transistors
• the base and collector of the first BJT are shorted together.
• the second BJT is coupled to the first BJT via a first resistor.
• the base of the third BJT is coupled to the collector of the first BJT.
• the base and collector of the fourth BJT are coupled together.
• a second resistor is coupled to the fourth emitter of the fourth BJT.
• a third resistor is coupled to the second resistor and to the emitter of the second BJT.
• An operational amplifier has a first input coupled to the first resistor and the collector of the second BJT, a second input coupled to the emitter of the third BJT and the collector of the fourth BJT, and an output coupled to the collectors of the first and third BJTs.
• FIG. 1 is a circuit schematic depicting an illustrative bandgap reference circuit in various examples.
• FIG. 2 is a circuit of an operational amplifier included in the bandgap reference circuit of FIG. 1.
• FIG. 3 is a circuit schematic of an implementation of a stage of the operational amplifier.
• FIG. 4 is a circuit schematic depicting an alternative embodiment of a bandgap reference circuit.
• bandgap reference voltage supplies provide constant, high-precision reference voltages in the face of various fluctuating parameters, including ambient temperature. Many bandgap reference voltage supplies operate on the principle of offsetting the negative temperature coefficient of one circuit with a positive temperature coefficient of another circuit.
• Bandgap reference voltage supplies include a complementary to absolute temperature (CTAT) voltage source coupled in series to a proportional to absolute temperature (PTAT) voltage source.
• CTAT complementary to absolute temperature
• PTAT proportional to absolute temperature
• the voltage is directly related to temperature (as temperature increases, the voltage also increases, and vice versa). Because the CTAT voltage source’s voltage changes in the opposite direction as the PTAT voltage source with changes in temperature, the resulting output voltage of the bandgap reference supply remains approximately unchanged.
• Such bandgap reference voltage supplies suffer from multiple sources of flicker noise.
• Some of the flicker noise arises from transistors (e.g., bipolar junction transistors, BJTs) in the voltage supplies, but this type of flicker noise may be addressed by adding a resistor between the base and collector of each BJT.
• Most of the remainder of the flicker noise arises from the base currents of the input transistor pair of the operational amplifier included within the bandgap reference voltage supply.
• the operational amplifier’s input transistor pair may generate flicker noise that is low frequency (e.g., 0. lHz to 10 Hz).
• Such low-frequency noise can be difficult to eliminate because one technique for eliminating the low frequency noise is to use large filter capacitors, which may not be practical in low-power applications.
• a bandgap reference circuit that includes a bandgap network coupled to an operational amplifier. At least one of the transistors within the bandgap network is configured to function also as part of a gain stage.
• the transistor is a BJT configured as a common-emitter amplifier.
• FIG. 1 is a circuit schematic diagram of an illustrative bandgap reference circuit 100.
• the bandgap reference circuit in FIG. 1 includes transistors Ml, M2, M3, and M4, resistors Rl, R2, and R3, and an operation amplifier OP1.
• the combination of transistors Ml and M2 and resistor Rl functions as the gain stage 150, mentioned above.
• transistors M1-M4 are NPN BJTs.
• the operational amplifier OP1 has a non-inverting (positive) input, an inverting (negative) input, and an output 123.
• the output 123 of operational amplifier OP1 provides the output bandgap voltage (VBG) from the bandgap reference circuit 100.
• VBG output bandgap voltage
• the output 123 of operational amplifier OP1 is coupled to the collectors of transistors Ml and M3.
• the bases of transistors Ml and M3 are coupled together and to their collectors.
• Resistor R1 is coupled between the emitter of transistor Ml and the collector of transistor M2.
• the connection between resistor R1 and the collector of transistor M2 is labeled node A.
• the non-inverting input of operational amplifier OP1 is coupled to node A, and thus to resistor R3 and to the collector of transistor M2.
• Transistor Ml is larger than transistor M3 as indicated by the sizing ratio “N: 1” where N is an integer greater than 1. Transistor Ml being N times as large as transistor M3 means that transistor Ml comprises N transistor fingers whereas transistor M3 has one transistor.
• N is 8. In another example N is 24.
• Transistor M2 is smaller than transistor M4 as indicated by the sizing ratio “1:N ” Accordingly, transistor Ml is N times larger than transistor M3, and similarly, transistor M4 is N times larger than transistor M2.
• Vbe_M 3 Vbe_M 3 — Vbe_M 1
• Vbe_M 3 the Vbe for transistor M3
• Vbe_M l the Vbe for transistor Ml.
• the Vbe of an individual BJT is a CTAT voltage
• the difference in Vbe’s between transistors M3 and Ml is a PTAT voltage.
• the thermal voltage VT is equal to kT/q, where T is temperature (in units of Kelvin), q is the charge on an electron, and k is Boltzman’s constant. Because VT is a function of temperate T, the thermal voltage (VT) is a PTAT voltage and thus the AVbe between transistors M3 and Ml also is a PTAT voltage.
• the AVbe between transistors M3 and Ml is the voltage VI across resistor Rl, which means that the voltage across resistor R1 is a PTAT voltage.
• the current through resistor Rl is shown in FIG. 1 as II and is AVbe /Rl. Because the voltage VI is a PTAT voltage, the current II is a PTAT current.
• the voltage across resistor R2 (shown as V2) is the AVbe between transistors M2 and M4.
• voltage V2 also is a PTAT voltage.
• the current through resistor R2 (shown as 12) is a PTAT current.
• the current through resistor R3 is shown as 13 and is the sum of currents II and 12. Because currents II and 12 are PTAT currents, current 13 also is a PTAT current. Accordingly, the voltage V3 across resistor R3 is a PTAT voltage, while the Vbe of each of the transistors M1-M4 are CTAT voltages.
• bandgap reference circuit 100 Starting from the ground terminal and progressing up the circuit to the voltage VBG, bandgap reference circuit 100 includes a PTAT voltage V3 in series with a CTAT Vbe voltage for transistor M2, an approximately zero voltage drop between the non-inverting and inverting inputs of the operational amplifier OP1, and a CTAT Vbe voltage for transistor M3. Similarly, the circuit includes a series combination of the PTAT voltage V3 and CTAT Vbe voltages for transistors M4 and Ml.
• the base of transistor M4 being coupled to the collector of transistor M4 configures transistor M4 as a diode.
• the base and collector of transistor M4 are coupled to node B and to the inverting input of amplifier OP1.
• the base of transistor M2 is not coupled to the collector of transistor M2, and instead is coupled to the base and collector of transistor M4 and thus also to the inverting input of operational amplifier OP1.
• transistor M2 also functions as a common-emitter amplifier, the input of which is the base of transistor M2 and the output is its collector (node A).
• the combination of transistor Ml, resistor Rl, and transistor M2 is operative as a gain stage 150 as represented by the dashed box.
• the transconductance of transistor Ml is represented as gm_Ml and the transconductance of transistor M2 is represented as gm_M2.
• the configuration of the bandgap circuit 100 to include the gain stage 150 advantageously results in flicker noise generated within the operation amplifier OP1 being attenuated by the factor gm_M2 * R.
• FIG. 2 shows a circuit schematic including additional detail of operational amplifier OP1.
• operational amplifier OP1 includes a first stage 210 coupled to a second stage 250.
• the first stage 210 includes a transconductance circuit 211 (having a transconductance value of GM0) coupled to a capacitor CO.
• the second stage 250 includes transistors M21-M24 and gain elements AP and AN coupled together to form a super source-follower buffer.
• transistors M21-M23 are P-type metal oxide semiconductor field effect transistors (PMOS transistors) and transistor M24 is an N- type metal oxide semiconductor field effect transistor (NMOS transistor).
• the output voltage VBG is the voltage on the source of transistor M21.
• the second gain stage 250 is configured for unity gain albeit with an offset voltage due to the gate-to-source voltage (Vgs) of transistor M21.
• FIG. 2 also shows an example of a start-up circuit 220 that includes transistors M25-M28 and a resistor R20.
• the start-up circuit 220 sets the gate voltage of transistor M22 to one threshold voltage (Vt) of the transistor below a chosen threshold voltage value, for example, Vthresh.
• Vt threshold voltage
• transistor M22 will be OFF. This results in transistor M23 of the second stage 250 to slew and rapidly charge up the load capacitor CL as well as the bandgap core.
• VBG becomes larger than Vthresh
• M22 turns ON and the second stage 250 shifts from slew mode to source-follower mode, in which the bandgap loop starts regulating VBG and brings it to its final steady state value.
• the voltage Vthresh is chosen such that the final VBG-Vthresh is slightly greater than the drain-to-source saturation voltage (VDS.SAT) of transistor M21 so as to keep transistor M21 operating in the saturation region.
• Setting the gate voltage of transistor M22 to Vthresh-Vt is achieved by passing a pre-generated AVbe/R (where R is the sum of the resistance of resistor R20 and any other resistors along the current path through M28 to ground) current through a series of diode-connected BJTs (e.g., transistor M28) and resistors and tapping from a node between them (see dashed line from the collector of transistor M28 to the gate of transistor M22.
• the start up circuit 220 also injects current and tries to pull-up nodes A and B (sources of transistors M25 and M26) with the help of M25 and M26.
• the start-up circuit 220 is configured such that transistors M25 and M26 turn off when the voltage on nodes A and B become close to their steady state value.
• the first stage 210 may be configured to have a relatively high gain.
• FIG. 3 shows an example implementation of the first stage 210.
• the first stage 210 includes a bias circuit 310 coupled to an amplifier 350.
• the bias circuit 310 generates various bias voltages such as PBIAS PTAT for use in the amplifier 350.
• the amplifier 350 includes an input transistor pair 352 which includes transistors M31 and M32.
• transistors M31 and M32 are PNP transistors.
• the base of transistor M31 is the non-inverting input which is coupled to node A in FIG. 1.
• the base of transistor M32 is the inverting input which is coupled to node B in FIG. 1.
• the sizing ratio between transistors M31 and M32 is the same as for the transistor pairs of FIG. 1 ( e.g ., 1:N).
• the Vbe voltage of each of transistors M31 and M32 is different due to the different sizes of the transistors.
• the voltage difference between the base of transistor M31 and the base of transistor M32 i.e., between the non-inverting and inverting inputs of the operational amplifier OP1 is the difference between the Vbe voltages of transistors M31 and M32.
• the sizing ratio between the corresponding pair of input transistors was 1:1, but in the example of FIG. 3 the sizing ratio is 1 :N.
• the voltage VI across resistor R1 is AVbejOPl — Vbe_M3> — Vbe_Ml, where AVbe OPl is the difference in Vbe voltages between transistors M31 and M32.
• the Vbe difference between transistors M31 and M32 adds and extra value of AVbe into the voltage VI across resistor Rl. Because the voltage VI is greater due to the additional AVbe from the operational amplifier’s first stage 210 (compared to what voltage VI would have been if the input pair M31 and M32 were identically sized), the current II in FIG. 1 increases, and consequently the summed current 13 also increases. To maintain the same PTAT voltage V3 across resistor R3 for the increased current 13, the resistance value of resistor R3 is decreased (e.g., by a factor of 2).
• a gain of (1 -I - ) is applied to the noise generated within the operational amplifier OP1. i?l
• An advantage of configuring the operational amplifier OP1 to present an extra AVbe voltage across resistors Rl and R2 is that the resistance R3 can and should be decreased to maintain the same PTAT V3 voltage and the same level of VBG.
• the noise of the operational amplifier OP1 is further attenuated.
• FIG. 4 is a circuit schematic depicting an alternative embodiment to that shown in FIG. 1.
• FIG. 4 is a schematic of a bandgap reference circuit 400 that includes transistors M41, M42, M43, and M44, resistors R41, R42, and R43, and an operational amplifier OP2.
• the transistors M41-M44 in bandgap reference circuit 400 are PNP BJTs.
• the operation of the bandgap reference circuit 400 largely is the same as that of bandgap reference circuit 100 in FIG. 1.
• Transistors M41 and M42 and resistor R41 form a gain stage 450, which is operative to attenuate flicker noise generated internal to operational amplifier OP2 in much the same way as the gain stage 150 of FIG. 1.
• Transistor M42 in FIG. 4 also functions as an amplifier in much the same way that transistor M2 of FIG. 1 was operative as an amplifier.
• the term “couple” may cover connections, communications, or signal paths that enable a functional relationship consistent with this description. For example, if device A generates a signal to control device B to perform an action: (a) in a first example, device A is coupled to device B by direct connection; or (b) in a second example, device A is coupled to device B through intervening component C if intervening component C does not alter the functional relationship between device A and device B, such that device B is controlled by device A via the control signal generated by device A.
• a device that is “configured to” perform a task or function may be configured (e.g., programmed and/or hardwired) at a time of manufacturing by a manufacturer to perform the function and/or may be configurable (or re-configurable) by a user after manufacturing to perform the function and/or other additional or alternative functions.
• the configuring may be through firmware and/or software programming of the device, through a construction and/or layout of hardware components and interconnections of the device, or a combination thereof.
• terminal As used herein, the terms “terminal”, “node”, “interconnection”, “pin” and “lead” are used interchangeably. Unless specifically stated to the contrary, these terms are generally used to mean an interconnection between or a terminus of a device element, a circuit element, an integrated circuit, a device or other electronics or semiconductor component.
• a circuit or device that is described herein as including certain components may instead be adapted to be coupled to those components to form the described circuitry or device.
• a structure described as including one or more semiconductor elements such as transistors), one or more passive elements (such as resistors, capacitors, and/or inductors), and/or one or more sources (such as voltage and/or current sources) may instead include only the semiconductor elements within a single physical device (e.g., a semiconductor die and/or integrated circuit (IC) package) and may be adapted to be coupled to at least some of the passive elements and/or the sources to form the described structure either at a time of manufacture or after a time of manufacture, for example, by an end-user and/or a third-party.
• semiconductor elements such as transistors
• passive elements such as resistors, capacitors, and/or inductors
• sources such as voltage and/or current sources
• MOSFET metal-oxide-silicon FET
• BJTs bipolar junction transistors
• Circuits described herein are reconfigurable to include the replaced components to provide functionality at least partially similar to functionality available prior to the component replacement.
• Components shown as resistors are generally representative of any one or more elements coupled in series and/or parallel to provide an amount of impedance represented by the shown resistor.
• a resistor or capacitor shown and described herein as a single component may instead be multiple resistors or capacitors, respectively, coupled in parallel between the same nodes.
• a resistor or capacitor shown and described herein as a single component may instead be multiple resistors or capacitors, respectively, coupled in series between the same two nodes as the single resistor or capacitor.
• ground in the foregoing description include a chassis ground, an Earth ground, a floating ground, a virtual ground, a digital ground, a common ground, and/or any other form of ground connection applicable to, or suitable for, the teachings of this description. Unless otherwise stated, “about,” “approximately,” or “substantially” preceding a value means +/- 10 percent of the stated value. Modifications are possible in the described examples, and other examples are possible within the scope of the claims.

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