Linear channel select filter

• US 20040128340A1
• Filed: 04/09/2003
• Published: 07/01/2004
• Est. Priority Date: 12/27/2002
• Status: Active Grant

• Current Assignee: Solum Co., Ltd.
• Original Assignee: Samsung Electro-Mechanics Co., Ltd. (Samsung Group)
• Inventors: Oh, Seung Min, Na, Yoo Sam, Kwon, Hyo Seok, Choi, Ki Won
• Granted Patent: US 7,177,895 B2
• Time in Patent Office: Days
• US Class Current: 708/819
• CPC Class Codes: H03H 11/1291 Current or voltage controlled filters

Abstract

A linear channel select filter having a simple structure is used for an IF selector of a satellite broadcasting tuner, linearly changes a desired frequency by adjusting an output current, and includes a GM current cell unit determining a control voltage according to a select signal, generating an output current according to an differential input voltage, linearly controlling the output current according to the control voltage, and providing a linearly variable resistance according to the linearly controlled output current, and a capacitor circuit coupled to the GM cell unit to provide a capacitance to generate a cutoff frequency voltage according to the output current and the variable resistance. An occupying area and a size of the filter is reduced.

Claims

1. a linear channel select filter selecting a desired frequency using a resistor and a capacitor, comprises:

a GM current cell controller determining a control voltage according to a selection signal, providing an output current according to a differential input voltage, linearly controlling the output current according to the control voltage, and providing a linearly variable resistance according to the linearly controlled output current; and

a capacitor circuit coupled to the GM current cell controller to provide a capacitance to generate a cutoff frequency voltage in accordance with the variable resistance.

2. The linear channel select filter of claim 1, wherein the GM current cell unit comprises:

a control voltage generator generating the control voltage determined according to the select signal; and

an output current controller generating the output current according to the differential input voltage, linearly controlling the output current according to the control voltage, and providing the linearly variable resistance according to the linearly controlled output current.

3. The linear channel select filter of claim 2, wherein the control voltage generator comprises:

a resistance circuit having a plurality of resistors between a reference potential and ground;

a switch unit having a plurality of switches to select corresponding ones of the resistors of the resistance circuit; and

a voltage generating unit generating the control voltage according to a resistance value determined according to the selected resistor of the resistance circuit.

4. The linear channel select filter of claim 2, wherein the output current controller comprises:

a current generating unit generating the output current according to the differential input voltage; and

a current control unit linearly controlling the output current io according to the control voltage generated from the control voltage generating unit.

5. The linear channel select filter of claim 2, wherein

a resistance circuit having a irst resistor unit having a plurality of first resistors coupled in series between the reference potential and the ground and a second resistor unit having a plurality of second resistors coupled between the corresponding adjacent first resistors;

a switch unit having a plurality of switches to select corresponding ones of the second transistors of the resistance circuit; and

a voltage generating unit having an operational amplifier having a positive terminal coupled to the second resistors of the second resistor unit, a negative terminal coupled to the ground, and an output terminal coupled to the negative terminal through a feedback resistor to generate the control voltage according to a ratio of a value of a resistance of the resistance circuit and a resistance of the feedback resistor generating the control voltage according to a resistance value determined according to the selected resistor of the resistance circuit.

6. The linear channel select filter of claim 2, wherein the output current controller comprises:

a first transistor having a first gate terminal coupled to a positive input terminal of the differential input signal and a first drain terminal coupled a voltage source;

a first current source coupled between the ground and a first source terminal of the first MOS transistor;

a second MOS transistor having a second drain terminal coupled to the voltage source and a second gate coupled between the ground and a negative terminal of the second MOS transistor; and

a second current source coupled between the ground and a second source terminal of the second MOS transistor.

7. A linear channel select filter selecting a desired frequency using a resistor and a capacitor, comprises:

a GM current cell controller having a first, input terminal receiving a selection signal, a second input terminal receiving an input voltage, a control voltage generator generating a control voltage according to the selection signal, an output current controller generating first and second currents according to the input voltage and generating a linearly variable resistance in response to the first and second currents to linearly generate an output current, and an output terminal outputting the linearly generated the output current; and

a capacitor circuit coupled to output terminal of the GM current cell controller to provide a capacitance to generate a voltage signal corresponding to the desired frequency according to the linearly generated output current.

8. The linear channel select filter of claim 7, wherein the output current controller comprises:

a current generating unit generating the first and second currents according to the input voltage; and

a current control unit generating the linearly variable resistance in response to the first and second currents to linearly generate the output current.

9. The linear channel select filter of claim 8, wherein the output current controller comprises a voltage source and first and second current sources, and the current generating unit comprises:

a first transistor coupled to the voltage source and the first current source input voltage to generate the first current; and

a second transistor coupled to the voltage source and the second current inpout voltage to generate the second current.

10. The linear channel select filter of claim 9, wherein the input voltage comprises positive and negative components, and the first transistor comprises:

a first gate terminal coupled to a positive component of the input voltage;

a first drain terminal coupled a voltage source; and

a source terminal coupled to a first current source to generate the first current.

11. The linear channel select filter of claim 10, wherein the second transistor comprises:

a second gate terminal coupled to the negative component of the input voltage;

a second drain terminal coupled to the voltage source; and

a second source terminal coupled to the second current source to generate the second current.

12. The linear channel select filter of claim 9, wherein the current control unit is coupled between the first and second transistors.

13. The linear channel select filter of claim 9, wherein the current control unit comprises:

a third transistor having a drain terminal coupled between the first transistor, a source terminal coupled to the second transistor, and a gate terminal coupled to the control voltage generator to receive the control voltage.

14. The linear channel select filter of claim 7, wherein the selection signal is a digital signal, and the control voltage generator comprises:

a D/A converter converting the digital signal to an analog signal corresponding to the control voltage.

15. The linear channel select filter of claim 7, wherein the control voltage generator comprises:

a differential amplifier generating the control voltage in response to the analog signal.

16. The linear channel select filter of claim 15, wherein the differential amplifier comprises:

a non-inverting input terminal receiving the analog signal;

an inverting input terminal receiving a voltage potential; and

an voltage output terminal outputting the control voltage according to the analog signal and the voltage potential.

17. The linear channel select filter of claim 16, wherein the differential amplifier comprises:

a feedback resistor coupled between the voltage output terminal and the inverting input terminal.

18. The linear channel select filter of claim 17, wherein the output current is proportional to a difference between the first and second currents.