To apply a desired voltage at a node driving a load impedance, a voltage source providing the desired voltage is connected to the node. In addition, a current source supplying an amount of current that would be drawn by the impedance if the voltage source alone were connected across the impedance. As a result, the voltage source may be freed substantially from supplying current, which may be advantageously used in several situations. For example, the approach can be used to connect a voltage source directly to a high load without potentially requiring a buffer between the voltage source and the node. Alternatively, the approach can be used to apply the same desired voltage at each of multiple nodes connected in series using the same voltage source without being affected by the routing resistance generally present between each pair of the nodes.
An up-converter 124 frequency-up-converts an analog signal Sm. A down-converter 121 frequency-down-converts analog signal Sm. A signal selection block 125 selects one of the frequency-up-converted signal Sfu and frequency-down-converted signal Sfd. The signal Se selected by the signal selection block 125 is provided to the primary winding of a transformer 127. A signal induced in the secondary winding of the transformer 127 is provided to an A/D converter 128 to produce a digital signal Dm. For example, if the analog signal Sm has DC or a low frequency close to DC, the signal Sfu is selected as the signal Se. If the analog signal Sm does no have DC nor a low frequency close to DC, the signal Sfd is selected as the signal Se.
A voltage source providing a constant reference voltage, independent of load variations at an output terminal. The effective impedance (looking-in impedance) at the output terminal is designed to be independent of frequency of the signals at the output terminal. In an embodiment, the resistance of one of two parallel impedance paths constituting the effective impedance is made equal to the resistance of the other path, and the time constants of both paths are made equal. As a result, the effective impedance is made independent of frequency, and the strength of the reference voltage is maintained constant without exhibiting ringing, DC droop, etc., despite load variations.
