Attenuator using variable resistors
Certain aspects of the present disclosure are directed towards a signal processing circuit. The signal processing circuit generally includes: an impedance transformation circuit coupled between a first node and a second node; and an attenuation circuit including a first variable resistive element coupled between the first node and a reference potential node, and a second variable resistive element coupled between the second node and the reference potential node.
1. A signal processing circuit, comprising:
an impedance transformation circuit coupled between a first node and a second node; and
an attenuation circuit including:
a first variable resistive element including a first attenuation transistor coupled between the first node and a voltage rail; and
a second variable resistive element including a second attenuation transistor coupled between the second node and the voltage rail.
2. The signal processing circuit of claim 1 , wherein the impedance transformation circuit includes:
a first inductive element coupled between the first node and a reference potential node;
a second inductive element coupled between the second node and the reference potential node; and
a capacitive element coupled between the first node and the second node.
3. The signal processing circuit of claim 1 , wherein the impedance transformation circuit includes:
a first capacitive element coupled between the first node and a reference potential node;
a second capacitive element coupled between the second node and the reference potential node; and
an inductive element coupled between the first node and the second node.
4. The signal processing circuit of claim 1 , further comprising a bias transistor coupled between the voltage rail and at least one of a base of the first attenuation transistor or a base of the second attenuation transistor.
5. The signal processing circuit of claim 4 , wherein the bias transistor is coupled between the voltage rail and the bases of the first attenuation transistor and the second attenuation transistor.
6. The signal processing circuit of claim 4 , further comprising a current source coupled to a current path, the current path being coupled to a base of the bias transistor.
7. The signal processing circuit of claim 1 , wherein:
the first variable resistive element further comprises a first resistive element coupled between the first node and an emitter of the first attenuation transistor; and
the second variable resistive element further comprises a second resistive element coupled between the second node and an emitter of the second attenuation transistor.
8. The signal processing circuit of claim 1 , further comprising:
an amplification transistor; and
a capacitive element coupled between the attenuation circuit and a base of the amplification transistor.
9. The signal processing circuit of claim 1 , wherein:
in a high-power mode (HPM) associated with the signal processing circuit, at least one of the first variable resistive element or the second variable resistive element is configured to have a first resistance; and
in a low-power mode (LPM) associated with the signal processing circuit, at least one of the first variable resistive element or the second variable resistive element is configured to have a second resistance less than the first resistance.
10. A wireless device, comprising:
a controller configured to determine a power mode associated with signal transmission;
an attenuator comprising:
a first variable resistive element coupled between a first node and a reference potential node or a voltage rail; and
a second variable resistive element coupled between a second node and the reference potential node or the voltage rail, wherein the controller is configured to bias the first variable resistive element and the second variable resistive element to generate an attenuator signal based on an input signal;
an impedance transformation circuit coupled between the first node and the second node; and
an amplifier coupled to the attenuator and configured to generate a signal for transmission based on the attenuator signal.
11. The wireless device of claim 10 , wherein:
the first variable resistive element includes a first attenuation transistor coupled between the first node and the voltage rail; and
the second variable resistive element includes a second attenuation transistor coupled between the second node and the voltage rail.
12. The wireless device of claim 11 , wherein the controller is further configured to turn off the first attenuation transistor and the second attenuation transistor based on the power mode being a high-power mode (HPM).
13. The wireless device of claim 11 , wherein, to bias the first variable resistive element and the second variable resistive element, the controller is configured to bias, via a bias circuit, the first attenuation transistor and the second attenuation transistor based on the power mode being a low-power mode (LPM).
14. The wireless device of claim 13 , wherein the bias circuit comprises a bias transistor coupled between the voltage rail and at least one of a base of the first attenuation transistor or a base of the second attenuation transistor.
15. The wireless device of claim 14 , wherein the bias transistor is coupled between the voltage rail and the bases of the first attenuation transistor and the second attenuation transistor.
16. The wireless device of claim 14 , wherein, to bias the first variable resistive element and the second variable resistive element, the controller is configured to control a current source to provide a current to a current path coupled to a base of the bias transistor.
17. A method for signal processing, comprising:
receiving an input signal; and
generating, via an attenuation circuit, an attenuator signal based on the input signal, the attenuation circuit comprising:
a first variable resistive element including a first attenuation transistor coupled between a first node and a voltage rail; and
a second variable resistive element including a second attenuation transistor coupled between a second node and the voltage rail, wherein an impedance transformation circuit is coupled between the first node and the second node.
18. The method of claim 17 , further comprising generating an amplified signal based on the attenuator signal via an amplification transistor coupled to the second node.
19. The method of claim 17 , further comprising:
determining a power mode associated with signal amplification; and
controlling the first variable resistive element and the second variable resistive element based on the power mode.
20. The method of claim 19 , further comprising turning off the first attenuation transistor and the second attenuation transistor based on the power mode being a high-power mode (HPM).
21. The method of claim 19 , further comprising biasing, via a bias circuit, the first attenuation transistor and the second attenuation transistor based on the power mode being a low-power mode (LPM).
22. The method of claim 21 , wherein the bias circuit comprises a bias transistor coupled between the voltage rail and at least one of a base of the first attenuation transistor or a base of the second attenuation transistor.
23. The method of claim 22 , wherein the bias transistor is coupled between the voltage rail and the bases of the first attenuation transistor and the second attenuation transistor.
24. The method of claim 22 , wherein biasing the first attenuation transistor and the second attenuation transistor includes sourcing, via a current source of the bias circuit, a current to a current path coupled to a base of the bias transistor.
25. The method of claim 17 , wherein:
the first variable resistive element further comprises a first resistive element coupled between the first node and an emitter of the first attenuation transistor; and
the second variable resistive element further comprises a second resistive element coupled between the second node and an emitter of the second attenuation transistor.
26. The method of claim 17 , wherein the impedance transformation circuit includes:
a first inductive element coupled between the first node and a reference potential node;
a second inductive element coupled between the second node and the reference potential node; and
a capacitive element coupled between the first node and the second node.
27. The method of claim 17 , wherein the impedance transformation circuit includes:
a first capacitive element coupled between the first node and a reference potential node;
a second capacitive element coupled between the second node and the reference potential node; and
an inductive element coupled between the first node and the second node.