| 摘要 |
<p>A voltage clamp circuit 25 comprises a group of Darlington connected bipolar transistors (Tr[1] to Tr[M], Fig. 2) is series with a group of diode-connected MOS transistors (PMOS[1] to PMOS[N]). Use of the diode-connected MOS transistors in place of some of the Darlington connected bipolar transistors of a prior art voltage clamp (Figs.7,8) avoids the clamping action being interfered with by a parasitic transistor (Fig. 2) associated with a diode-connected transistor Tr(0) which acts as a rectifier/detector connected to a resonance circuit 10, C3 of a non-contact information card used in an automatic ticket clipping system. An electromagnetic wave from a reader/writer (2, Fig.6) is applied to the card for writing and reading data to/from the card and for supplying power to the card. A digital signal processor 15 receives input data from the resonance circuit, and turns a transistor 11 on and off to change the resonance frequency of the resonance circuit for reading out data. The power supply for the card includes a smoothing capacitor C5 and a voltage regulator 13.</p> |
