Apparatus for removing DC offset and amplifying signal with variable gain simultaneously

• US 7,227,409 B2
• Filed: 04/26/2005
• Issued: 06/05/2007
• Est. Priority Date: 11/25/2004
• Status: Expired due to Fees

• Current Assignee: Sunplus Technology Co., Ltd
• Original Assignee: Sunplus Technology Co., Ltd
• Inventors: Chung, Yuan-Hung
• Primary Examiner(s): NGUYEN, KHANH V
• Application Number:
  US11/115,686
• Publication Number:
  US 20060109050A1
• Time in Patent Office: 770 Days
• Field of Search: None
• US Class Current: 330/69
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 2203/45522 the FBC comprising one or more potentiometers
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/45968 by offset reduction

Abstract

An apparatus for removing DC offset and variable gain amplifying simultaneously is provided. A signal voltage level of the output terminal of the first amplifier module is A times that of the first input terminal of the first amplifier module. A voltage level of an output DC offset signal of the first low-pass filter circuit is B times that of the input signal of the first low-pass filter circuit. The output signal of the second amplifier module is a sum of a C1-time amplified first input signal of the second amplifier module and a C2-time amplified second input signal of the second amplifier module, which satisfy the following equation:
A×B×C1=−C2.

Claims

1. An apparatus for removing DC offset and amplifying signal with variable gain simultaneously, comprising:

a voltage following circuit for providing a reference voltage level;

a first amplifier module, comprising;

a first resistance, comprising one terminal coupled to a positive input signal;

a first operational amplifier, comprising an inverting terminal coupled to another terminal of the first resistance; and

a second resistance, comprising one terminal coupled to the inverting terminal of the first operational amplifier, and another terminal coupled to an output terminal of the first operational amplifier;

a first filter circuit, comprising;

a third resistance, comprising one terminal coupled to the output terminal of the first operational amplifier;

a first capacitor, comprising one terminal coupled to one terminal of a fourth resistance, and another terminal connected to ground;

a second amplifier module, comprising;

a fourth resistance, comprising one terminal coupled to the positive input signal;

a fifth resistance, comprising one terminal coupled to an output terminal of the first filter circuit;

a second operational amplifier, comprising a non-inverting input terminal coupled to the voltage following circuit and an inverting input terminal coupled to another terminals of the fourth resistance and the fifth resistance; and

a sixth resistance, comprising one terminal coupled to the inverting terminal of the second operational amplifier, and another terminal coupled to an output terminal of the second operational amplifier;

wherein the fourth resistance is R4, the first resistance is R1, the second resistance is R2 and the fifth resistance is R5, and wherein

$R_4=R_5\times <br><br>\frac{R_1}{R_2}.$

2. The apparatus according to claim 1, wherein the voltage following circuit comprises:

a seventh resistance, comprising one terminal coupled to the non-inverting input terminals of the first operational amplifier and the second operational amplifier, and another terminal coupled to the positive input signal;

a eighth resistance, comprising one terminal coupled to the non-inverting input terminals of the first operational amplifier and the second operational amplifier, and another terminal coupled to a negative input signal; and

a second capacitor, comprising one terminal coupled to the non-inverting input terminals of the first operational amplifier and the second operational amplifier, and another terminal connected to ground;

wherein the seventh resistance is R7 and the eighth resistance is R8, and wherein R7=R8.

3. The apparatus according to claim 1, wherein the apparatus is suitable for a communication receiving device.

4. The apparatus according to claim 3, wherein the communication receiving device is a zero intermediate frequency receiver.

5. The apparatus according to claim 1, wherein the voltage following circuit is a reference voltage provider.

6. The apparatus according to claim 1, wherein the sixth resistance is a variable resistance.

7. The apparatus according to claim 1, wherein the first capacitor is a variable capacitor.

8. The apparatus according to claim 1, wherein the first capacitor comprises a metal-oxide-semiconductor field effect transistor.

9. The apparatus according to claim 1, further comprising:

a third amplifier module, comprising;

a ninth resistance, comprising one terminal coupled to the negative input signal;

a third operational amplifier, comprising an inverting input terminal coupled to another terminal of the ninth resistance, and a non-inverting terminal coupled to the voltage following circuit; and

a tenth resistance, comprising one terminal coupled to the inverting input terminal of the third operational amplifier, and another terminal coupled to an output terminal of the third operational amplifier;

a second filter circuit, comprising;

an eleventh resistance, comprising one terminal coupled to the output terminal of the third operational amplifier; and

a third capacitor, comprising one terminal coupled to another terminal of the eleventh resistance, and another terminal connected to ground;

a fourth amplifier module, comprising;

a twelfth resistance, comprising one terminal coupled to the negative input signal;

a thirteenth resistance, comprising one terminal coupled to the output terminal of the second filter circuit;

a fifth operational amplifier, comprising a non-inverting input terminal coupled to the voltage following circuit, and an inverting input terminal coupled to another terminals of the twelfth resistance and the thirteenth resistance; and

a fourteenth resistance, comprising one terminal coupled to the inverting input terminal of the fourth operational amplifier, and another terminal coupled to an output terminal of the fourth operational amplifier;

wherein the twelfth resistance is R12, the ninth resistance is R9, the tenth resistance is R10 and the thirteenth resistance is R13, and wherein

$R_{12}=R_{13}\times <br><br>\left(\frac{R_9}{R_{10}}\right).$

10. The apparatus according to claim 7, wherein the fourteenth resistance is a variable resistance.

11. The apparatus according to claim 7, wherein the third capacitor is a variable capacitor.

12. The apparatus according to claim 7, wherein the third capacitor comprises a metal-oxide-semiconductor field effect transistor.

13. An apparatus for removing DC offset and amplifying signal with variable gain simultaneously, comprising:

a first amplifier module, comprising a first input terminal and an output terminal, wherein the first input terminal of the first amplifier module is coupled to a positive input signal comprised of a positive DC offset signal and a normal signal, and a voltage level of an output signal from the output terminal of the first amplifier module is A times that of the first input terminal of the first amplifier module;

a first low-pass filter circuit, comprising an input terminal and an output terminal, wherein the input terminal of the first low-pass filter circuit is coupled to the output terminal of the first amplifier module, which in turn outputs B-time amplified positive DC offset signal and filters the B-time amplified normal signal;

a second amplifier module, comprising a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the second amplifier module is coupled to the output terminal of the first low-pass filter circuit and the second input terminal of the second amplifier module is coupled to the positive input signal, a second output signal of the second amplifier module being a sum of an amplified C1-time first input signal of the second amplifier module and an amplified C2-time second input signal of the second amplifier module, wherein A, B, C1, C2 are non-zero real numbers and wherein A×

B×

C1=−

C2.

14. The apparatus according to claim 13, further comprising:

a third amplifier module, comprising a first input terminal and an output terminal, wherein the first input terminal of the third amplifier module is coupled to a negative input signal comprised of a negative DC offset signal and the normal signal, a voltage level of a third output signal of the third amplifier module being A times that of the first input terminal of the third amplifier module;

a second low-pass filter circuit, comprising an input terminal and an output terminal, wherein the input terminal of the second low-pass filter circuit is coupled to the output terminal of the third amplifier module, which in turn outputs the B-time amplified negative DC offset signal and filters the B-time amplified normal signal; and

a fourth amplifier module, comprising a first input terminal, a second terminal and an output terminal, wherein the first input terminal of the fourth amplifier module is coupled to the output terminal of the second low-pass filter circuit and the second input terminal of the fourth amplifier module is coupled to the negative input signal, a fourth output signal of the fourth amplifier module being a sum of an amplified C1-time first input signal of the fourth amplifier module and an amplified C2-time second input signal of the fourth amplifier module.

15. The apparatus according to claim 14, further comprises a voltage following circuit coupled to the positive input signal and the negative input signal to output a reference voltage, wherein the first amplifier module further comprises a second input terminal, the second amplifier module further comprises a third input terminal, the third amplifier module further comprises a second input terminal and the fourth amplifier module further comprises a third input terminal, all input terminals being connected to ground.

16. The apparatus according to claim 13, wherein the apparatus is suitable for a communication receiving device.

17. The apparatus according to claim 16, wherein the communication receiving device is a zero intermediate frequency receiver.