Patent EP-0018918-B1 (EP)
IPC: H03M1/00
Filed: 1980-05-06
Granted: 1983-05-25
Abstract: 1. A digital-analog conversion circuit having a sinusoidal characteristic, of the type comprising : - a terminal for receiving a reference voltage U defining the analog conversion scale, - digital input terminals for receiving a series (b1 to bn-2 ) of numbers representing, in a predetermined weight order, the numerical value of an angle at least in fractions of a quadrant, - an amplifier-inverter, - a first set of resistors which are arranged to form a potential divider, one end terminal of which is connected to the output of the amplifier-inverter, and the middle terminal is connected to the inverting input of the amplifier-inverter, - a second set of resistors forming a digital-analog converter network, and - a switching assembly capable of interconnecting selectively, under the effect of switching control means as a function of the input numbers, the first and second set of resistors so as to provide at the analog output of the amplifier-inverter an approximation by straight-line segments of a sinusoidal function of the numerical value of the input, characterised in that the first set of resistors comprises a resistance (Rpo ) connected on one side to the output of the amplifier-inverter, and a number m greater than or equal to 1, of resistive dividers (Rsc , Rpc ) mounted between the reference voltage terminal and the output of the amplifier-inverter, the switching assembly comprises a first switching device having at least two contacts (Sd ) connected on the one hand to the other side of the first mentioned resistor (Rpo ) and to the centre point of the resistive divider or dividers (Rsc , Rpc ) respectively, and on the other hand, in common to the input of the amplifier-inverter, the second set of resistors arranged in parallel between the reference voltage terminal and the input of the amplifier-inverter comprises further resistors (R1 to R8 ) arranged in series with respective contacts (S1 to S8 ) forming a second switching device in the switching assembly, and switching control means act on the condition of the contacts of the first and second switches respectively as a function of at least one greater weight and the other lesser weights of the numerical value applied to the input terminals, one and one alone of the contacts of the first switch being closed each time, and with K designating a predetermined factor, epsilon designating a small approximation quantity selected in advance, and Rmin representing the resistor equivalent to the parallel assembly of the resistors (R1 to R8 ) of said second set, - the resistor Rpo is substantially equal to : K/U . Rmin . sin(pi/2 . 1/m+1+epsilon/2) the resistor or resistors Rpc , according to the value of their index c, are substantially equal to : K/U . Rmin . [sin(pi/2 . c+1/m+1+epsilon/2)- sin(pi/2 . c/m+1+epsilon/2)] - and the resistor or resistors Rsc , according to the value of their index c, are substantially equal to U/K . 1/sin(pi/2 . c/m+1+epsilon/2) . Rpc , the analog output of the amplifier then forming an approximation by straight line segments over a quadrant of a sinusoidal function of the numerical value of the input.