Abstract:
The present invention refers to a digital analogical converter comprising a sigma delta cascade modulator having two outputs, particularly a third order sigma delta modulator 2+1. In an embodiment the digital analogical converter comprises: a sigma delta modulator (1) of the type having two outputs (67, 68) able to supply a first (Y1) and a second (Y2) signal to said two outputs (67, 68); a reconstruction circuit (2) of first said (Y1) and second (Y2) signal able to provide a reconstructed signal (Yout); a filter (3) able to filter said reconstructed signal (Yout); characterized in that said reconstruction circuit (2) combines said first (Y1) and second (Y2) signals according to the following relationship Yout= Y1* (1+ Z -1 ) - Y2* (1- Z -1 ) + Y2* Z -2 * (1- Z -1 ) where Yout corresponds to said reconstructed signal, Y1 corresponds to said first signal, Y2 corresponds to said according to signal, Z corresponds to the Z transform.
Abstract:
Fully-differential, switched-capacitor circuit having a first and second input terminal (5a, 5b), and including: an operational amplifier (2, 41) having a first and a second differential input (4a, 4b), a first and a second output terminal (8a, 8b) and a bias control terminal (17); a feedback network (9a, 9b), connected between the differential outputs (8a, 8b) and the input terminals (5a, 5b), and having intermediate nodes connected to the differential inputs (4a, 4b) of the operational amplifier (2, 41); and a control circuit (3), including a detection network (19) and an error amplifier (20, 21). The error amplifier (20) has a first input receiving a desired common-mode voltage (V XID ), and an output connected to the bias control terminal (17) and supplying a control voltage (V XC ). The detection network (19) has a first and a second input connected directly, respectively, to the second input terminal (4a, 4b) of the operational amplifier (2, 41), and an output connected to a second input of the error amplifier (20), and supplying a common-mode drive voltage (V XCM ).
Abstract:
A method of improving the signal/noise ratio of a sigma-delta modulator during the re-establishment of its stability which comprises the following steps: defining a bit sequence corresponding to a state of instability of the modulator, monitoring the flow of bits output by the modulator to check whether it contains the instability bit sequence, and resetting the modulator to zero if the instability bit sequence is detected at the output. To ensure a high signal/noise ratio of the modulator even during the detection and re-establishment of stability, the method also comprises the following steps: delaying the flow of bits output by the modulator at least for the time required to detect the instability bit sequence and modifying the output bit sequence during the delay period by replacing it with a predetermined bit sequence.
Abstract:
The present invention refers to a completely differential operational amplifier of the folded cascode type. In one embodiment the completely differential operational amplifier of the folded cascode type comprises: a differential output stage (15, 16, 17, 18, 19, 20 21, 22); a differential input stage (11, 12) able to drive said output stage (15, 16, 17, 18, 19, 20 21, 22); said differential output stage (15, 16, 17, 18, 19, 20 21, 22) includes a first branch (15, 16, 17, 18) having at least a first (16) and a second (17) transistor, and a second branch (19, 20 21, 22) having at least a third (20) and a fourth (21) transistor; said first (15, 16, 17, 18) and second (19, 20 21, 22) branch are coupled to a first (VDD) and to a second (GND) feeding voltage; a feedback circuit (40) of said first (16), second (17), third (20) and fourth (21) transistors; characterized in that said feedback circuit (40) is constituted by a single amplifier (40) having four inputs (IN1, IN2, IN3, IN4) and four outputs (OUT1, OUT2, OUTS, OUT4), said four inputs (IN1, IN2, IN3, IN4) take the voltage present on a terminal (23, 13, 24, 14) of said first (16), second (17), third (20) and fourth (21) transistors, and said four outputs (OUT1, OUT2, OUT3, OUT4) provide each a voltage to the control elements of said first (16), second (17), third (20) and fourth (21) transistors, which depend on the value of the input voltage of said four inputs (IN1, IN2, IN3, IN4).