Sub-ranging analogue to digital converter using differential signals and direct current subtraction

摘要

PCT No. PCT/GB91/00508 Sec. 371 Date Sep. 28, 1992 Sec. 102(e) Date Sep. 28, 1992 PCT Filed Apr. 2, 1991 PCT Pub. No. WO91/15899 PCT Pub. Date Oct. 17, 1991.An analogue to digital converter comprising a first analogue to digital conversion stage (14) for performing a relatively coarse conversion on a sample of an analogue input signal; a sample and hold stage (13) for holding the sample of the analogue signal fed to the first conversion stage while it is converted by the first conversion stage; a digital to analogue conversion stage (15) to which the digital output from the first conversion stage is fed; a difference circuit (16) for generating an analogue difference signal representing the difference between the signal held by the sample and hold stage (13) and the output from the digital to analogue conversion stage (15); a second analogue to digital conversion stage (17) for generating a digital output corresponding to the difference signal; and a combining unit (18) for combining the digital outputs of the first and second conversion stages to generate a digital output representing the sampled analogue input signal. The sample and hold stage (13) and the first and second analogue to digital conversion stages (14, 17) each responds to a respective pair of differential input signals. The sample and hold (13) and digital to analogue conversion stages (15) each generate output signals in the form of differential pairs of currents. The difference circuit (16) arithmetically combines appropriate pairs of the currents from the sample and hold and digital to analogue conversion stages to generate a differential current pair for input to the second analogue to digital conversion stage.