High-speed analog-digital converter having a signal folding structure improved by reducing the number of elementary cells
The invention relates to high-resolution analog-digital converters using so-called folding differential amplifier structures composed of differential circuits (crossed differential pairs) and of loads (cascode transistors). The folding structure according to the invention comprises, in the case where it is desired to produce four curves folded at two periods in the useful range of voltages to be converted, four folding blocks (one per curve). The first comprises 7 differential circuits and eight loads, the end loads not being linked to the output of the block. The other blocks comprise 6 differential circuits and eight loads, the last load of each block not being linked to the output of this block. Gains are achieved in terms of bulk, consumption and operating speed, with respect to existing structures.
1. An analog-digital converter with signal folding circuits, comprising at least two folding blocks, each block comprising a series of N+1 differential circuits of rank 1 to N+1, with N integer, and a series of N+2 load circuits of rank 1 to N+2 associated with the differential circuits of each series, the differential circuits of each block being juxtaposed and linked to one another by their outputs, each differential circuit having four inputs and two outputs, the first output of a differential circuit of rank j being linked to the second output of a preceding differential circuit of rank j−1 of the series and the second output of the differential circuit considered being linked to the first output of the following differential circuit of rank j+1, a first load circuit of rank j being linked to the first output of the differential circuit considered of rank j, this load circuit being shared with the preceding differential circuit of rank j−1 of the series, and a second load circuit of rank j+1 being linked to the second output of the differential circuit concerned of rank j, this load circuit being shared with the following differential circuit of rank j+1 of the series, the load circuits of even rank having an output connected to a first common output of the series and the load circuits of odd rank having an output connected to a second common output of the series, wherein there are provided for all the blocks an additional differential circuit of rank N+2 and an additional load circuit of rank N+3 connected to the second output of the additional differential circuit, the output of the latter load circuit not being linked to a common output of the series, and in that there is furthermore provided, in the first folding block, a differential circuit of rank 0 and a load circuit of rank 0 connected to the first output of the differential circuit of rank 0, the output of the load circuit of rank 0 not being linked to a common output of the first block.
2. The converter as claimed in claim 1 , wherein the differential circuits each comprises a double differential pair of transistors, a transistor of one pair having its collector linked to the collector of a transistor of the other pair and vice versa.
3. The converter as claimed in claim 1 , wherein the load circuits comprise a cascode transistor and a follower transistor, with the exception of the load circuits of rank N+3 and of rank 0 which comprise only a cascode transistor but no follower transistor.