Communications: electrical – Audible indication – Percussion-type sound producer
Patent
1980-12-19
1982-09-28
Miller, Charles D.
Communications: electrical
Audible indication
Percussion-type sound producer
H03K 1302
Patent
active
043520936
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a high-speed digital/analog converter. It is used in electronics, for example in the signal processing field and more specifically in high throughput digital/analog conversion and in amplitude modulation with several levels and a high throughput.
A digital/analog converter is a circuit in which an analog magnitude E corresponds to a classified system of bits a.sub.k in accordance with the equation: ##EQU1## in which the symbol k designates the rank of the bits varying from 0 to n-1 and the coefficient Eo is a reference magnitude. Generally, the analog magnitude is of an electrical nature (current or voltage).
The block diagram of a digital/analog converter is shown in FIG. 1. Such a circuit comprises n current generators 10.sub.0, 10.sub.1 . . . 10.sub.k . . . 10.sub.n-1 and n switches 12.sub.o, 12.sub.1 . . . 12.sub.k, . . . 12.sub.n-1. The generators are able to supply currents I.sub.0, I.sub.1 . . . I.sub.k . . . I.sub.n-1, whose values are in the form:
The bits of the digital signal to be converted determine the state (switched on or off) of the circuit switches. A zero bit controls the switching off of the corresponding switch and a bit equal to 1 its switching on. The total current I.sub.s supplied by such a circuit is therefore in the form: ##EQU2## the above expression being identical to that of equation (1).
The current generators most frequently encountered in this application are shown in FIG. 2. They comprise a transistor 14, a diode 16, a resistor 18 of value R.sub.k and two resistors 20 and 22 of values R.sub.1 and R.sub.2. The circuit is completed by two supply connections at voltages V.sub.cc and V.sub.EE. The useful voltage is the current I.sub.k of the transistor collector.
The circuit operates as follows. Diode 16 compensates the base-emitter displacement voltage of transistor 14. The voltage V.sub.E at the terminals of resistor 18 is then equal to the voltage V.sub.E at the terminals of resistor 22. On ignoring the base current compared with the collector current, it is possible to write: ##EQU3##
In order to form a digital/analog converter with such generators, it is merely necessary to associate therewith a series with the resistors R.sub.k forming a geometrical progression of ratio 1/2:R.sub.k =R/2.sup.k.
The total current I.sub.s is then: ##EQU4##
The present invention relates to such as converter, but which operates at a higher speed than the prior art converters described hereinbefore.
To this end, the current generators and switches are constructed in a special way in accordance with the so-called "coupled emitter technology" (or abbreviated to ECL for Emitter-coupled logic).
Before describing the features of the invention, the principles of ECL integrated circuits are briefly described. Bipolar logic circuits can be distributed into two basic categories, as a function of their operating mode. The first category includes saturated logics (resistor, transistor logic RTL, diode, transistor logic DTL and transistor, transistor logic TTL), whilst the other category covers the non-saturated logics coupled in the current mode (current mode logic CML, emitter-coupled logic ECL and emitter-coupled, current slaved logic ECCSL).
The present invention uses a circuit type belonging to the second category, namely the ECL type. Such a logic circuit is shown in FIG. 3 in the case of a NOR quadruple. It comprises a first purely logic stage formed from four logic gates (30.sub.0, 30.sub.1, 30.sub.2, 30.sub.3) each having two inputs respectively (E.sub.oa, E.sub.ob)(E.sub.1a, E.sub.1b) (E.sub.2a, E.sub.2b) and (E.sub.3a, E.sub.3b) and one output respectively (S.sub.0, S.sub.1, S.sub.2, S.sub.3) and a second current amplification stage formed by four transistors 32.sub.0, 21.sub.1, 32.sub.2 and 32.sub.3, each having a base b, an emitter e and a collector c, the base of one transistor being connected to the output of the preceding logic gate.
The circuit also has a first supply line 34 at a voltage V.sub.cc1, said line being connected to all the collectors c of the t
REFERENCES:
patent: 2869115 (1959-01-01), Doeleman
patent: 2956272 (1960-10-01), Cohler
patent: 2994862 (1961-08-01), Preston
patent: 3217147 (1965-11-01), Chapman
patent: 3299315 (1967-01-01), McMillan
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