Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
  • G05F1/10—Regulating voltage or current
  • G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
  • G05F1/462—Regulating voltage or current wherein the variable actually regulated by the final control device is dc as a function of the requirements of the load, e.g. delay, temperature, specific voltage/current characteristic
  • G05F1/463—Sources providing an output which depends on temperature
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
  • G05F1/10—Regulating voltage or current
  • G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
  • G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
  • G05F1/565—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor
  • G05F1/567—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor for temperature compensation
• • 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
  • G05F3/18—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using Zener diodes

Definitions

• This invention relates to temperature-compensated Zener-diode voltage references. More particularly, this invention relates to a so-called “auto-TC" voltage refer ⁇ ence wherein trimming of a circuit resistance to give a predetermined output voltage will simultaneously optimize the temperature compensation for that output voltage.
• the present invention in one preferred embodiment provides an auto-TC voltage reference wherein an opera ⁇ tional amplifier receives at one input the voltage of a Zener diode and at its other input receives a compensation signal from a feedback circuit comprising a transistor and resistor network.
• a feedback circuit comprising a transistor and resistor network.
• FIGURE 1 is a graph showing the temperature- response characteristics of Zener diodes made by the same process
• FIGURE 2 is a schematic to illustrate the func ⁇ tioning of a voltage reference in accordance with the invention
• FIGURE 3 shows a modified circuit based on Figure 2 but utilizing only a single transistor in the feedback network
• FIGURE 4 presents a generalized schematic diagram to illustrate further aspects of the invention
• FIGURE 5 is a circuit diagram showing a circuit design suitable for an integrated circuit
• FIGURE 6 is a circuit diagram showing a modifica ⁇ tion to the circuit of Figure 5.
• the graph of Figure 1 depicts in an idealized manner the temperature response characteristics of the avalanche voltage (V z ) versus temperature of a group of Zener diodes produced by the same process.
• the slopes of upper and lower solid lines 10 and 12 illustrate extremes of positive and negative temperature coefficients (TC) respectively. Any one diode made by the process can have a TC which lies anywhere between these extremes. It will be assumed in the following discussion that the temperature response characteristic is linear, which is approximately correct as a practical matter.
• T m is shown as being negative on the absolute or Kelvin scale, which is generally true in practice. Although such a negative T m is not a realizable operating point, it is useful for analysis as an extrapolation of Zener behavior in a normal operating temperature range.
• V z v m + a l ( ⁇ ⁇ m ) where: V z is the avalanche voltage
• V m is a voltage parameter which is rela ⁇ tively insensitive to variations in a given process (and typically is in the range of 4.4V to 4.8V for a number of known processes) ,
• T m is a temperature parameter which is relatively insensitive to variations in a given process
• ⁇ - ⁇ is a parameter with a value associ ⁇ ated with each fabricated device. Its variability from unit to unit encompasses most of the avalanche voltage variations which result from process variability.
• This circuit includes an operational amplifier 20 having its non-inverting input terminal 22 connected to the positive electrode of a Zener diode 24 producing a voltage V 2 .
• the other Zener electrode is connected to a common line 26.
• the Zener voltage generally is temperature sensitive, as discussed above with reference to Figure 1.
• the output terminal 28 of the amplifier 20 pro ⁇ Jerusalem an output voltage V 0 responsive to the applied Zener voltage.
• a negative feedback circuit generally indicated at 30 is connected between the output terminal 28 and the common line 26.
• This feedback circuit 30 includes a number of series-connected elements comprising a first segment 32 with a resistor Rl and diode Dl, a second segment 34 with a resistor R2 and a diode D2, and a resistor R3.
• the junc ⁇ tion point 36 between the two segments 32, 34 is connected to the inverting input terminal 38 of the amplifier 20.
• the output V 0 will be temperature invariant. However, because there is a diode in each feedback segment 32, 34, and because the V ⁇ E of a diode has a negative TC, the current in the feedback circuit nevertheless will vary with temperature.
• the initial value of R2 can be set significantly less than Rl (R2 ⁇ Rl) , and R2 can be thought of as R2 "nominal" in series with an initially negative R3 of rela ⁇ tively large value.
• the circuit without any trimming should be capable of compensating for a limiting (maximum) positive TC in the Zener 24.
• R2 can be trimmed up (increased in ohmic value) until the correct magnitude is reached to provide compen ⁇ sation for the actual Zener involved (including Zeners with negative TC) .
• the range of Zener TC which can be compensated is constrained by the relationship between the diode V BE and the magnitude of the Zener voltage V z which determines the maximum TC of the current in Rl and R2. To increase this range, more diodes can be added to both feedback segments 32, 34.
• V BE multiplier of known configuration, as shown at 40 in Figure 3 (and also as described in Brokaw Patent 4,622,512).
• the V BE of transistor Q4 appears across resistor R6, and the accompanying current through R6, R5 and R4 produces a multiplied version of that V BE across resistors R5 and R4.
• the feedback voltage for input terminal 38 is tapped off an intermediate point 36A between R4 and R5.
• the V BE of one transistor can be "multiplied” to provide effective junction drops in both feedback segments 32A and 34A.
• the V BE is effectively multiplied by (1 + (R4 + R5)/R6) ,
• V Q can be made a convenient value higher than V m .
• the nominal value of V Q to which the output will be trimmed must be higher than the maximum anticipated Zener voltage by an amount which allows for the temperature compensation voltage.
• R2 200 (initially)
• the output voltage V Q changed only about 4 millivolts peak-to-peak, in a convex curve centered rough ⁇ ly about 6 volts, with the output lower than 6V at both ends of the curve.
• a V Q of 6 volts at room temperature was obtained when R2 was trimmed to 4.56K.
• the output changed by only about 5mV peak-to-peak over the same 180° tempera ⁇ ture sweep, in a curve which was inverted relative to the positive TC Zener curve.
• the cir ⁇ cuit provided auto-TC for Zener diodes with either positive or negative TC.
• Rl can be chosen to give any nominal cur ⁇ rent through the feedback network at a given temperature. Since V_ has a TC proportional to its value, the TC of the current can be adjusted by adjusting V c . Thus it is possible to independently choose the current and the TC of the current, over some range. This is what makes it possi ⁇ ble to find a single value of R3 which compensates both the TC of V Q to zero (or nearly so) and simultaneously sets the output voltage at (1 + k)V m .
• V c the value of V c will achieve this condi ⁇ tion.
• the Zener has a voltage V JJJ and zero TC. In this case, it will not be necessary to adjust R3 away from zero, the feedback ratio will be (1 + k) at all temperatures, and both V ⁇ and V Q will equal (1 + )V m .
• V BE has a negative TC and its voltage extrapo ⁇ lates to go through the bandgap voltage (approximately 1.2V) at 0°K.
• V c to be a multiple of V ⁇ E makes it possible to develop such a voltage which extra ⁇ polates to V m at T m .
• Using k times this multiple of V BE as the voltage source in the upper segment 34B of the feedback completes the compensation so that trimming R3 to bring V Q to (1 + k)V m should also cause the TC of V Q to be zero.
• the magnitude of V c is set by the values of the resistors in the feedback network.
• the total voltage across all three feedback resistors R4, R5 and R6 similarly will be 6V, since that is the selected output voltage.
• the resistance ratio (R5 +R6)/R4 will be as follows:
• V ⁇ E multiplier should produce a total of about 4 V BE s, with one V ⁇ E across R6, about two V BE s across R5, and about one V ⁇ E across R4.
• the output V Q must also be 6V, with zero TC, at all other operating points. This is because the characteristics of all of the elements in the circuit have been assumed to be linear, so that their summation or differencing must also be a linear relationship.
• V o V x + V 3
• V 0 (V m + 1 (T-T m ) (1 + k) + (R3/R1) (at ! - ⁇ 2 ) (T-T m )
• V m (1+k) ⁇ (T-T m )(l+k) + (R3/Rl)( ttl - ⁇ 2 )(T-T m )
• the first term of this expression is the same as the nominal value of V Q for which the circuit is intend ⁇ ed. To get V 0 to the nominal value, R3 must be adjusted to make the remaining terms zero.
• the temperature dependence can be divided out with the factor (T-T m ) to give:
• V c is not a battery, but something constructed of forward-biased diode drops. Therefore, it must have some bias current to operate which implies that the voltage across Rl must be positive for all operating temperatures and bias condi ⁇ tions. Presumably T-T m will always be positive, since T m is often less than 0° Kelvin.
• V BE V GO (V GO - V BE ⁇ ) + ln ⁇ + ⁇
• the largest component of this expression is the second term which is linear in T.
• the third term usually reduces the effect of the fourth term, although the circuit described here does not force a strictly PTAT collector current as is often done in bandgap circuits.
• V ⁇ E In the auto-TC circuit disclosed herein, it is necessary to extrapolate the behavior of V ⁇ E back to T m , the Zener temperature parameter.
• an extrapolated voltage for V ⁇ E at T m can be calculated. Denoting this value V E , the ratio of V m to V E will determine the "number" of V ⁇ E s to be produced across R5 and R6.
• the value of R6 can be selected from biasing considerations by determining how much of the total current in Rl can be diverted to R4, R5 and R6.
• R5 R6 ( (V m /V E )-1) .
• This will cause the voltage across R5 and R6 to approximate the function V m + ⁇ 2 (T-T m ) where 2 is a multiple of the design temperature TC of V ⁇ E .
• An error will result from the base current of the transistor Q4, but this will generally be small. If low ⁇ is a problem, the error can be reduced by using an integral number of diode connected transistors less than V ⁇ /V- g , and multiplying only one to get any fractional part (see Figure 6) .
• FIG. 5 presents a detailed circuit diagram of a voltage reference in accordance with this invention and suitable for adaptation to IC format.
• a dashed-line box 20 indicates the operational amplifier, as shown in the some ⁇ what simplified diagrams previously discussed.
• the feed ⁇ back circuit 30A is of the V BE -multiplier type described with reference to Figure 3.
• a start-up circuit 46 is pro ⁇ vided in the usual way.
• Figure 6 presents a modified form of feedback cir ⁇ cuit 30C for the voltage reference of Figure 5, to reduce errors due to base current in the V BE multiplier transis ⁇ tor Q4.
• a pair of diode-connected transistors Q10 and Qll have been connected in series with the transistor Q4 to produce the required integral number of V BE s, with the fractional part for the lower feedback segment being supplied by the V BE multiplier across R5.
• an additional transistor-connected diode Q5 has been inserted between R4 and R2 with the fractional part of V BE - or ⁇ e u PP er segment appearing across R4.
• the volt ⁇ age between the network junction point 36C and the top of Rl will be about 3-1/3 V BE s.

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• Electromagnetism (AREA)
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• Automation & Control Theory (AREA)
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• 1992
  • 1992-08-20 WO PCT/US1992/007039 patent/WO1993004423A1/fr active IP Right Grant
  • 1992-08-20 EP EP92918698A patent/EP0600003B1/fr not_active Expired - Lifetime
  • 1992-08-20 DE DE69230856T patent/DE69230856T2/de not_active Expired - Lifetime
  • 1992-08-20 JP JP5504594A patent/JPH06510149A/ja active Pending

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