The assumption used in eq. Another variation of the present invention is the circuit in FIG. According to yet still a further embodiment of the present invention, the current multiplier subcircuit of the yet a further embodiment is rearranged to minimize bias and control circuitry and yet still provide extrinsic series resistance compensation. According to another embodiment of the present invention, a proportional-to-absolute-temperature sensor circuit is constructed in which two parallel current paths each contain two stacked series transistors. Proportional-to-absolute-temperature PTAT temperature sensors and bandgap reference circuits determine their output values based upon the difference in the voltage drops on diode junctions having different current densities. Hall effect device with epitaxal layer resistive means for providing temperature independent sensitivity. A subcircuit including three bipolar transistors is substituted in place of a single bipolar transistor to achieve extrinsic base and emitter series resistance compensation in translinear circuits.
For a certain ratio of the resistors R 1 and R 2 , V BG becomes equal to the bandgap voltage, and it is essentially temperature independent. Because transistor Q 2 is larger in area than transistor Q 1 , the current densities in the junctions of transistor Q 2 are less by a factor of K than the corresponding densities in transistor Q 1 when the same total collector current I flows through both transistors. One sub-branch includes two stacked series transistors, while the other sub-branch includes a single transistor and includes the bandgap reference output feedback loop. This is a fairly reasonable assumption for quality bipolar transistors that maintain a constant current gain for many decades in current density. According to a further embodiment of the present invention, the equivalent subcircuit is substituted in the conventional Brokaw bandgap reference circuit to produce a bandgap reference circuit having extrinsic series resistance compensation. Conventional methods to provide extrinsic series base and emitter compensation are either inaccurate over differing operating conditions or involve complicated digital computations to provide adequate compensation. A classic example of a translinear circuit is the Brokaw bandgap circuit, shown in FIG.
A low-voltage bandgap circuit uses an operational amplifier feedback circuit with bipolar transistors having differing emitter areas and a voltage divider to generate base voltages for a Brokaw-type bandgap cell. The emitter areas of the four transistors are chosen so that the extrinsic series resistances through the two parallel current paths are equal and therefore cancel each other. Preferred implementations of the embodiments described involve whole number multiples of the emitter areas using unit transistors so that correct area ratios can be precisely controlled.
In this case the equivalent base-emitter voltage is given by the following. Because all transistors in this embodiment have zero base-collector voltages, errors associated with base width modulation are also eliminated. Bandgap voltage reference circuit with high power supply rejection ratio PSRR and curvature correction.
USB1 – Series resistance compensation in translinear circuits – Google Patents
It is straightforward that the errors due to the series resistors in the translinear loops are eliminated if all the iR drops cancel on the loop. The primary property exploited by these circuits is the exponential variation of the current density across a p-n junction barrier with the intrinsic voltage applied on that barrier.
However, for the circuit in FIG. In particular, it is very hard to control the ratio of these internal resistances to the other resistors in the circuit R 1 and R 2. The voltage drop on the emitter extrinsic series resistance is usually much lower than the term compensztion the base resistance.
If all the IR drops are ignored and Q 1 -Q 4 are matched devices at the compenastion temperature, eq. Another object of the present invention is to provide proportional-to-absolute-temperature sensor circuits and bandgap reference circuits which effectively compensate for the extrinsic base and emitter series resistances under all operating conditions.
Importantly, the cancellation of the output voltage temperature dependence is obtained independently of the absolute value of the resistors R 1 and R 2which is difficult to control.
US6225850B1 – Series resistance compensation in translinear circuits – Google Patents
It is noteworthy that the secondary loop works correctly if the IR drops are significantly higher than random V BE mismatches, and this is exactly the regime requiring IR voltage drops compensation. Since this secondary loop forces equal bias currents I equal to the main bias current I through each of the transistors Q 3 -Q 6with the emitter areas indicated, the equilibrium voltage drop between points C and B is as follows.
Field of the Invention The present invention relates to the field of translinear circuits, including current multipliers, bandgap reference circuits, and proportional-to-absolute-temperature sensor circuits. A classic example of a translinear circuit is the Brokaw bandgap circuit, shown in FIG.
Method and a measuring circuit for determining temperature from a PN junction temperature sensor, and a temperature sensing circuit comprising the measuring circuit and a PN junction.
The application of this technique to a bandgap reference circuit is shown in FIG. This assumption is based on the good practice of making integer multiplicity devices from matched transistors connected in parallel. Because this embodiment has circukts few elements between the positive supply and ground, this embodiment is suitable for low-voltage operation.
Another advantage of this implementation is the fact that all the bipolar transistors Q 1 -Q 7 are biased with zero base-collector voltage, thus reducing the errors associated with the base width modulation the Early effect.
The transistor Q 1 is replaced by the combination Q 11 -Q 13 and auxiliary circuitry that ensures the same collector current for all these transistors. Specifically, transistor Q 2 is K times larger in emitter area than transistor Q 1.
The extra bipolar transistor Q 7 has the same collector current as the other two branches through the feedback loop with the op amp A 2 detailed analysis confirms a perfect IR drop cancellation in the output voltage as follows.
The present invention relates to the field of translinear circuits, including current multipliers, bandgap reference circuits, and proportional-to-absolute-temperature sensor circuits. As yet another example, the multiplier cell in FIG.
An object of the present invention is to provide a general purpose extrinsic base and emitter series resistance compensation circuit effective in any translinear circuit. According to yet still a further embodiment of the present invention, the current multiplier subcircuit of the yet a further embodiment is rearranged to minimize bias and control circuitry and yet still provide extrinsic series resistance compensation.
This simplified analysis also neglects other second order effects, such as the lowering of the effective base resistance at high current densities due to emitter current crowding.
A subcircuit including three bipolar transistors is substituted in place of a rssistance bipolar transistor to achieve extrinsic base and emitter series resistance compensation in translinear circuits. The IR voltage drops in the bipolar transistors Q 1 -Q 4 are cancelled if the following relation is satisfied since all the Transinear drops are inversely proportional to emitter area.
Assuming series resistances inversely proportional to the emitter area, this equivalent base-emitter voltage is circuihs of IR voltage drops.
The translindar substitution is applied to a Brokaw-type translineqr cell. A feedback loop driven by the bandgap output voltage forces a fixed current through a voltage divider. A separate loop, consisting of bipolar transistors Q 3 -Q cirucitsthe operational amplifier A 2and the current sources I and 2 I also servo-ed from the main bias current I force a small voltage drop between the points B and C.
The emitter areas of the two transistors whose base to emitter voltages add are chosen so that their series extrinsic resistance is equal to the extrinsic resistance of resistancd third transistor which subtracts. A current multiplier, comprising:. According to another embodiment of the present invention, a proportional-to-absolute-temperature sensor circuit is constructed in which two parallel current paths each contain two stacked series transistors. Therefore, the initial circuit, with Q 1Q 2the current mirror I, and the op amp A 1 behaves as if the bipolar devices Q 1 and Q 2 would resisfance ideal base-emitter voltages V be.
Those errors are cancelled in the multiplier circuits proposed in FIG. Because transistor Q 2 sries larger in area than transistor Q 1the current densities in the junctions of transistor Q 2 are less by a factor of K than the corresponding densities in transistor Q 1 when the same total collector current I flows through both transistors. Conventional circuits for extrinsic base and emitter series resistance compensation suffer from the flaw the compensation resistor has a different temperature coefficient than the extrinsic base and emitter resistances because of the different fabrication and structural composition of the compensation resistor and the extrinsic base and icrcuits resistances.
A detailed analysis follows, using the emitter area ratios indicated. The same technique can be applied to any translinear circuit. The embodiments having more elements between the positive supply and ground require relatively higher supply voltages, but provide the capacity for larger output voltage dynamic swing.
This application is a divisional of Ser. The influence of base width modulation serries the base-collector voltage the Early effect on the collector current can also be minimized by cascode configurations or active biasing for constant V CB.
All the translinear circuits are based on the logarithmic variation of the intrinsic base-emitter voltage of a bipolar transistor with its collector current. The major difference consists in the fact that the bases of bipolar transistors Q 1 and Q 2 are not connected together to the output point B.
Several circuit topologies for bandgap circuits are also disclosed.