| 摘要 |
Apparatus for digitising an impedance is described that comprises a first impedance element (22; 122) having a first impedance (C1;A1) that varies with a property to be measured and a second impedance element (24; 124) having a second impedance (C2;A2). The apparatus also includes a drive signal generator (26,30) for applying a first alternating drive signal (44) to the first impedance element (22; 122) and a second alternating drive signal (46) to the second impedance element (24; 124). An analogue-to-digital converter, ADC (42; 142), receives a resultant signal (41;52; 141 ) comprising the combination of the signals produced by the application of the first and second alternating drive signals (44,46) to the first and second impedance elements (22,24; 122, 124). The first alternating drive signal (44) is phase shifted relative to the second alternating drive signal (46) such that the resultant signal (41;52;141) received and sampled by the ADC (42; 142) sequentially relates to the sum of, and the difference between, the first and second impedances. The apparatus also comprises a signal separator (56;156A,156B) that receives sample values from the ADC (42; 142) and generates a sum channel (58; 158A) and a difference channel (60; 160A) therefrom. |
