Impedance circuit and method for signal transformation
An impedance circuit includes an input terminal, a first and a second capacitive arrangement and an output terminal coupled to the input terminal by a network. The network includes the first and the second capacitive arrangement. The first capacitive arrangement includes a varactor circuit having a varactor and at least one series circuit. The at least one series circuit includes a capacitor and a switch in series connection and is coupled parallel to the varactor circuit. The second capacitive arrangement comprises an additional capacitor.
1. An impedance circuit, comprising:
an input terminal;
a first capacitive arrangement that comprises a varactor circuit having a varactor and a series circuit that comprises a capacitor and a switch in series connection, the series circuit coupled in parallel with the varactor circuit;
a second capacitive arrangement that comprises an additional capacitor; and
an output terminal coupled to the input terminal by a network that comprises the first capacitive arrangement and the second capacitive arrangement; and
a control circuit that controls the switch of the series circuit and controls the varactor circuit and comprising an input for receiving a control signal and an analog-to-digital converter coupled between the input of the control circuit and a control terminal of the switch of the series circuit,
wherein the analog-to-digital converter is realized as a pipe-line converter and comprises a first sub-circuit with a first comparator and a first subtraction unit and also comprises a second sub-circuit with a second comparator and a second subtraction unit such that output terminals of the first and the second comparators form an output of the analog-to-digital converter and wherein the analog-to-digital converter incorporates a generator such that an output of the second subtraction unit is connected to an output of the generator and the generator provides a generator signal that depends on a difference between the predetermined capacitance value of the first capacitive arrangement and the present capacitance value of the series circuit.
2. An impedance circuit, comprising:
an input terminal;
a first capacitive arrangement that comprises a varactor circuit having a varactor and a series circuit that comprises a capacitor and a switch in series connection, the series circuit coupled in parallel with the varactor circuit;
a second capacitive arrangement that comprises an additional capacitor;
an output terminal coupled to the input terminal by a network that comprises the first capacitive arrangement and the second capacitive arrangement; and
a control circuit configured to control the switch of the series circuit and to control the varactor circuit, the control circuit comprising an input configured to receive a control signal and an analog-to-digital converter coupled between the input of the control circuit and a control terminal of the switch of the series circuit,
wherein the analog-to-digital converter is designed as a parallel converter that comprises a first, a second and a third comparator and the control circuit comprises a generator coupled between the input of the control circuit and the varactor circuit, the generator configured to provide a generator signal that depends on the control signal and a capacitance value provided by the series circuit and wherein the generator comprises a summation unit and a subtraction unit such that the summation unit is coupled on its input side to output terminals of the first, the second and the third comparators, a first input of the subtraction unit is coupled to the input of the control circuit and a second input of the subtraction unit is connected to an output of the summation unit as well as an output of the subtraction unit forms an output of the generator.