Variable gain amplifier circuit, controller of main amplifier and associated control method

• US 9,654,074 B2
• Filed: 10/22/2015
• Issued: 05/16/2017
• Est. Priority Date: 05/31/2015
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Lin, Lai-Ching
• Primary Examiner(s): Mottola, Steven J
• Application Number:
  US14/919,737
• Publication Number:
  US 20160352298A1
• Time in Patent Office: 572 Days
• Field of Search: 330 86, 330140, 330282, 330285
• CPC Class Codes: H03F 1/0205 in transistor amplifiers
• CPC Class Codes: H03F 1/0277 Selecting one or more amplifiers from a plurality of amplifiers
• CPC Class Codes: H03F 1/223 with MOSFET's
• CPC Class Codes: H03F 1/301 in MOSFET amplifiers H03F1/303, H03F1/305, H03F1/308 take precedence
• CPC Class Codes: H03F 2200/462 the current being sensed
• CPC Class Codes: H03F 2200/78 A comparator being used in a controlling circuit of an amplifier
• CPC Class Codes: H03F 2203/45114 the differential amplifier contains another differential amplifier in its feedback circuit
• CPC Class Codes: H03F 2203/45116 Feedback coupled to the input of the differential amplifier
• CPC Class Codes: H03F 3/211 using a combination of several amplifiers H03F3/60 takes precedence
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence
• CPC Class Codes: H03G 3/30 in amplifiers having semiconductor devices

Abstract

A variable gain amplifier circuit comprises a main amplifier, a current sensing circuit, a variable loading and a control amplifier. The main amplifier is configured for amplifying an input signal to generate an output signal. The current sensing circuit is coupled to the main amplifier, and is configured for generating a sensed current related to a current flowing through the main amplifier. The variable loading is coupled to the current mirror via a node, wherein the sensed current flows through the node and the variable loading. The control amplifier is coupled to the node and the main amplifier, and is configured for receiving a control voltage and a voltage of the node to generate an adjustment signal to control a gain of the main amplifier, wherein a resistance of the variable loading has a nonlinear relationship with the control voltage.

Claims

1. A variable gain amplifier circuit, comprising:

a main amplifier, for amplifying an input signal to generate an output signal;

a current sensing circuit, coupled to the main amplifier, for providing a sensed current related to a current flowing through the main amplifier;

a variable loading, coupled to the current sensing circuit via a node, wherein the sensed current flows through the node and the variable loading to provide a loading voltage; and

a control amplifier, coupled to the node and the main amplifier, for receiving a control voltage and the loading voltage to generate an adjustment signal to control a gain of the main amplifier;

wherein a resistance of the variable loading has a nonlinear relationship with the control voltage; and

the variable loading comprises a plurality of circuit cells, and each of the circuit cells provides a specific current to the node, and a combination of the specific currents provided by the circuit cells is comprised of the sensed current flowing through the node and the variable loading.

2. The variable gain amplifier circuit of claim 1, wherein the resistance of the variable loading has an exponential relationship with the control voltage.

3. The variable gain amplifier circuit of claim 1, wherein the resistance of the variable loading has a polynomial relationship with the control voltage.

4. The variable gain amplifier circuit of claim 1, wherein a summation of the specific currents provided by the circuit cells is the sensed current flowing through the node and the variable loading.

5. The variable gain amplifier circuit of claim 4, wherein the specific currents provided by the circuit cells are the same.

6. The variable gain amplifier circuit of claim 4, wherein the circuit cells receives a plurality of reference voltages, respectively, and each circuit cell provides the specific current to the node when a specific voltage is greater than the received reference voltage, wherein the specific voltage is generated according to the control voltage inputted into the control amplifier.

7. The variable gain amplifier circuit of claim 6, wherein the plurality of reference voltages are not all the same.

8. The variable gain amplifier circuit of claim 7, wherein for the circuit cells, the smaller the received reference voltage, the larger the specific current provided to the node.

20. The variable gain amplifier of claim 1, wherein each of the circuit cells comprises:

a first N-type transistor;

a second N-type transistor, wherein a gate electrode of the second N-type transistor is coupled to a gate electrode of the first N-type transistor;

a first P-type transistor, wherein a gate electrode of the first P-type transistor is coupled to a reference voltage, and a drain electrode of the first P-type transistor is coupled to a drain electrode of the first N-type transistor;

a second P-type transistor, wherein a gate electrode of the second P-type transistor is coupled to a drain electrode of the second N-type transistor, and a source electrode of the first P-type transistor and a source electrode of the second P-type transistor are coupled to a terminal supplied by a reference current; and

a third N-type transistor, wherein a gate electrode and a drain electrode of the third N-type transistor is coupled to a drain electrode of the second P-type transistor;

wherein a current flows through the second N-type transistor serves as the specific current of the circuit cell.

9. A controller of a main amplifier, comprising:

a current sensing circuit, for generating a sensed current related to a current flowing through the main amplifier;

a variable loading, coupled to the current mirror via a node, wherein the sensed current flows through the node and the variable loading; and

a control amplifier, coupled to the node, for receiving a control voltage and a loading voltage of the node to generate an adjustment signal to control a gain of the main amplifier;

wherein a resistance of the variable loading has a nonlinear relationship with the control voltage; and

the variable loading comprises a plurality of circuit cells, and each of the circuit cells provides a specific current to the node, and a combination of the specific currents provided by the circuit cells is comprised of the sensed current flowing through the node and the variable loading.

10. The controller of claim 9, wherein the resistance of the variable loading has an exponential relationship with the control voltage.

11. The controller of claim 9, wherein the resistance of the variable loading has a polynomial relationship with the control voltage.

12. The controller of claim 9, wherein a summation of the specific currents provided by the circuit cells is the sensed current flowing through the node and the variable loading.

13. The controller of claim 12, wherein the specific currents provided by the circuit cells are the same.

14. The controller of claim 12, wherein the circuit cells receives a plurality of reference voltages, respectively, and each circuit cell provides the specific current to the node when a specific voltage is greater than the received reference voltage, wherein the specific voltage is generated according to the control voltage inputted into the control amplifier.

15. The controller of claim 14, wherein the plurality of reference voltages are not all the same.

16. The controller of claim 15, wherein for the circuit cells, the smaller the received reference voltage, the larger the specific current provided to the node.

21. The controller of claim 9, wherein each of the circuit cells comprises:

a first N-type transistor;

a second N-type transistor, wherein a gate electrode of the second N-type transistor is coupled to a gate electrode of the first N-type transistor;

a first P-type transistor, wherein a gate electrode of the first P-type transistor is coupled to a reference voltage, and a drain electrode of the first P-type transistor is coupled to a drain electrode of the first N-type transistor;

a second P-type transistor, wherein a gate electrode of the second P-type transistor is coupled to a drain electrode of the second N-type transistor, and a source electrode of the first P-type transistor and a source electrode of the second P-type transistor are coupled to a terminal supplied by a reference current; and

a third N-type transistor, wherein a gate electrode and a drain electrode of the third N-type transistor is coupled to a drain electrode of the second P-type transistor;

wherein a current flows through the second N-type transistor serves as the specific current of the circuit cell.

17. A method for controlling a main amplifier, comprising:

generating a sensed current related to a current flowing through the main amplifier;

providing a variable loading for receiving the sensed current at a node, wherein the variable loading comprises a plurality of circuit cells, and each of the circuit cells provides a specific current to the node, and a combination of the specific currents provided by the circuit cells is comprised of the sensed current flowing through the node and the variable loading; and

generating an adjustment signal according to a control voltage and a loading voltage of the node to control a gain of the main amplifier;

wherein a resistance of the variable loading has a nonlinear relationship with the control voltage.

18. The method of claim 17, wherein the resistance of the variable loading has an exponential relationship with the control voltage.

19. The method of claim 17, wherein the resistance of the variable loading has a polynomial relationship with the control voltage.

22. The method of claim 17, wherein each of the circuit cells comprises:

a first N-type transistor;

a second N-type transistor, wherein a gate electrode of the second N-type transistor is coupled to a gate electrode of the first N-type transistor;

a first P-type transistor, wherein a gate electrode of the first P-type transistor is coupled to a reference voltage, and a drain electrode of the first P-type transistor is coupled to a drain electrode of the first N-type transistor;

a second P-type transistor, wherein a gate electrode of the second P-type transistor is coupled to a drain electrode of the second N-type transistor, and a source electrode of the first P-type transistor and a source electrode of the second P-type transistor are coupled to a terminal supplied by a reference current; and

a third N-type transistor, wherein a gate electrode and a drain electrode of the third N-type transistor is coupled to a drain electrode of the second P-type transistor;

wherein a current flows through the second N-type transistor serves as the specific current of the circuit cell.