This invention relates to a current source arrangement comprising N (N.ltoreq.1) current sources I.sub.p (p=1, . . . , N) for generating N binary-weighted currents, said sources comprising 2.sup.N -1 substantially equal current source transistors which are arranged in a matrix comprising R rows and K columns of matrix elements each comprising M current source transistors such that RxKxM=2.sup.N, each current source I.sub.p comprising a plurality of 2.sup.p-1 current source transistors. The invention also relates to a digital-to-analog converter comprising such a current source arrangement.
If such a current source arrangement is used a digital-to-analog converter can be realized by applying the binary-weighted output currents via switches, controlled by the digital input code, to a summing point or by draining them to a power supply terminal. The sum current occurring at the summing point then constitutes the analog output signal corresponding to the digital input code.
An important property of such a D/A converter is the monotonicity, that is to say, the output current occurring at a given input code should be larger than or equal to the output current associated with the previous digital input code. If this is not the case, there is a monotonicity error. In D/A converters constituted by binary-weighted current sources, such monotonicity errors may easily occur, more specifically when a so-called carry bit occurs.
The monotonicity errors are caused by the inequality of the output currents of the current source transistors constituting the binary-weighted current sources. These inequalities may be caused, for example, by temperature gradients occurring across the integrated circuit.
A binary-weighted current source arrangement which reduces the detrimental effect of a linear temperature gradient across the integrated circuit on the mutual equality of the output currents of the current source transistors is known from U.S. Pat. No. 3,995,304. To this end the current source transistors are arranged in a matrix so that the distance between the current source transistors and the centre of the matrix increases as the intensity of the current source increases. However, such an arrangement of the current source transistors does not inhibit the detrimental effects of non-linear temperature gradients and gradients and variations of other physical quantities across the matrix surface area, such as doping concentration variations, oxide thickness variations and the like.