DD131702B1 - CIRCUIT WITH A VARIETY OF DIFFERENT ELECTRICITY GENERATORS - Google Patents

Description

_ Λ -

Klaus Storch TYPE H. 03 K / 199 444

E 571

IPK: E 03 K, 13/02 12.2.1978

Title of the invention

Circuit for digital-to-analog converter with, a plurality of juxtaposed current generators:

Field of application of the invention;

The invention relates to a method for digital-analog handler with a plurality of juxtaposed power generators. The differences in the currents of the individual power generators should therefore be kept as small as possible. Further, a high internal resistance of the power generators is desired.

Characteristic 'of the known technical solutions

A circuit having a multiplicity of identical emitter-connected transistors is known as current generators, one of which is regulated by the voltage tapped off by a measuring resistor and an operational amplifier, and the others by a common busbar potential rail.

Although this solution can reduce the T.Temperature drift with a favorable arrangement of the transistors, the respective absolute value of the currents is determined by the Ugg tolerances and the current gain differences Absolute error caused by Ug _E and remarkable for medium currents A complementary Darlington circuit only slightly improves this characteristic, and if the described disadvantage is eliminated by selected transistors, the relatively small internal resistance of the simple current source remains.

It is also conceivable, the temperature drift: in such: circuits to compensate for controlling, by assigning the temperature as an independent variable a corresponding reference voltage waveform. This is only at small, thermally and in the temperature error course strictly indentischen power generator en ;, aloo at. monolithic circuits can be used successfully.

It is also possible to provide each individual current generator with "a control loop :: (radio, television, electronics", 1977/8, "S" 266 ff.). If one uses an operational amplifier and has a low offset voltage and sufficient gain, the main disadvantage is only the high cost. If a simple differential amplifier is used, the accuracy is not high under practical operating conditions. The cause is an asymmetry of the differential stage due to regulation, which is also effective as a pinch voltage if both transistors are absolutely equal.

Aim of the invention

It is an object of the invention to use low-cost circuits; Create a variety of identical StrorageneratoreiL for digital-to-analog conversion su.

- 3 -

Explanation of the essence of the invention

The / invention is based on the object, the currents of a plurality of juxtaposed identical power generators, despite the scattering of the component characteristics by circuit measures using the fact that in different microelectronic technologies relative errors are easier to control than absolute error, as far as possible to equalize each other.

According to the invention, this object is achieved in power generators with measuring resistors, where the respective current is tapped as a voltage and with inputs to control this current by means of a voltage that pairs symmetrical differential amplifiers provided are: in each case an input of two adjacent differential amplifier together to a measuring resistor and the respectively associated: inverting outputs are connected in common to the input of the same: current generator, and that a ring circuit is provided in such a way that the first and the last half of the differential amplifiers arranged next to one another become a complete symmetrical ¹ . It is essential for the puncture of this circuit that initially no longer each current generator is connected to the reference voltage while the errors must be kept small as an absolute problem in the voltage-current conversion, but that a current each with, compared to an equal further stream and the difference is compensated. If, in addition to the relative accuracy, a stable absolute value of the currents is desired, it is sufficient, as usual, to compare a current with a reference element. The only difference: needed differential amplifier must have a sufficiently small input; Ria3 current, so as not to disturb the symmetry of the circuit. Further details of the circuit will be explained with reference to the embodiment.

embodiment

The attached drawing represents a circuit with four current generators arranged according to the invention, which, however, as can easily be seen, can be arbitrarily extended without loss of accuracy. The electricity generators; for the currents I _n о ··· I _n are controlled by Darlington circuits of npn trans. TU. ·· T- • - formed. The currents I _n -O ··· I-, are due to the voltage drop across the

Resistors R _c ... R _Q controllable and the measuring resistors э · о

IL,... ,, IL can be measured as tension. The differential amplifiers fg + To ··· ^ 8 ^{+ f &} i form control circuits which, however, do not compensate with respect to a reference voltage but allow the current difference of each of two adjacent current generators to approach zero Difference amplifier TU and 2? .. closed loop, there is a regulating puncture between all Stroißgeneratoren with the tendency to let the current differences are zero .. The differential ^amplifiers Τ ₂ ^{+ Ϊ} 3 ··· ⁵ 8 ^{+ T} 1 are thereby symmetrically loaded, too if the operating voltage or the reference voltage change as absolute values, this relative coincidence of the currents is achieved by, the following properties:

1. Strict symmetry of the circuit across all current generator em with control stage.

2. Purely identical resistors R ₁ to R, the current difference ZY / ischen 2 stages without the differential amplifiers would be determined as usual by the ü- ^ g differences of the Darlington stage. These are too high at rated current. The differential amplifiers T ₂ ⁺ T ¹ O ··· ^ з + ^ і cause a significantly lower current to flow, resulting in a small offset error over the gain, which is essentially lower. is determined by the resistors Rc to Rg, this small offset error is transferred to a small deviation to the current differences. Thus, the disadvantage of Darlingt-onanordnung is eliminated and the large current gain bsw, dor larger Innenwiders'oand can

used: v / earth.

By the use of: npn transistors, the circuit integration is joyful except the measuring resistors R ^ to R., which can be realized for higher accuracies sense in Dünnschichttjechnik.

It is possible to lower the requirements for the equality of the currents., While maintaining the principle of mutual stabilization, two current generators each; to include in the control loop a differential amplifier.

Claims (1)

Invention; sanspruch Circuit for digital-to-analog converter with; a plurality of juxtaposed current generators: with measuring resistors, at which the respective current can be tapped and with inputs for controlling this current by means of a voltage, characterized in that pairwise symmetrical differential amplifier (TU + T.,; T ^1. + T ₁ -; dV + T ,,; T ₀ + !,) are provided, wherein in each case an input of two adjacent differential amplifiers together (based on T ^ T ₂ ; ЗуьТ ^; ...} to a measuring resistor CR-, ϊ R ₂ I R->; R /) and their respective inverting outputs (collector of ^ + T ₂ ; T ₃ HT ₄ ; ..,) together to the input (R ₅ ; R ₆ ; R ^; Rg) of the same current generator ^(Т Э ^{+ Т 1О;} ^ іТ ^ іг ^'Ф 13 ^{+ Т' і4; Т} connected 15 ^{+ аг 1б} ^, and that a ring circuit actual provided such that the first (T ₁₎ and the last half (Tg) of the arranged adjacent to each other Differential amplifier δχχ a complete * balanced differential amplifier (T., + I ₈ ) is connected. For this purpose / j page drawing