Circuit and method of signal frequency conversion

• US 6,263,199 B1
• Filed: 12/14/1998
• Issued: 07/17/2001
• Est. Priority Date: 12/14/1998
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wortel, Klaas, Welty, Dennis L.
• Primary Examiner(s): Hunter, Daniel
• Assistant Examiner(s): Nguyen, Thuan T.
• Application Number:
  US09/211,168
• Time in Patent Office: 946 Days
• Field of Search: 455/333, 455/190.1, 455/192.2, 455/313, 455/319, 455/323, 455/326, 455/330, 327/116, 327/356, 327/358, 327/359
• US Class Current: 455/333
• CPC Class Codes: H03D 2200/0033 Current mirrors
• CPC Class Codes: H03D 2200/0084 Lowering the supply voltage and saving power
• CPC Class Codes: H03D 7/1441 using field-effect transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1458 Double balanced arrangements, i.e. where both input signals are differential

Abstract

A mixer (20) has a differential transistor pair (22, 24) receiving first and second reference currents at first and second nodes (30, 34). An RF signal drives the differential transistor pair. A first switching circuit (44, 46) is coupled to the first node and a second switching circuit (52, 54) is coupled to the second node. An LO signal drives the first and second switching circuits. The first and second switching circuit each have first and second outputs that are cross-coupled at output nodes (48, 50) to provide a differential IF output current representative of the sum and difference between the frequency of the RF signal and the frequency of the LO signal.

Claims

1. A frequency conversion circuit, comprising:

a differential transistor circuit having first and second inputs coupled for receiving an input signal and first and second conduction terminals coupled to first and second nodes for receiving first and second reference currents;

a first switching circuit having an input coupled to the first node, a control input coupled for receiving a local oscillator signal, and first and second outputs coupled to first and second outputs of the frequency conversion circuit;

a second switching circuit having an input coupled to the second node, a control input coupled for receiving the local oscillator signal, and first and second outputs coupled to the first and second outputs of the frequency conversion circuit; and

a current mirror circuit having an input coupled to the first output of the frequency conversion circuit and an output coupled to the second output of the frequency conversion circuit for providing a single-ended output signal of the frequency conversion circuit.

2. The frequency conversion circuit of claim 1 wherein the first switching circuit includes:

a first transistor having a first conduction terminal coupled to the first node, a second conduction terminal coupled to the first output of the frequency conversion circuit, and a control terminal coupled for receiving a first component of the local oscillator signal; and

a second transistor having a first conduction terminal coupled to the first node, a second conduction terminal coupled to the second output of the frequency conversion circuit, and a control terminal coupled for receiving a second component of the local oscillator signal.

3. The frequency conversion circuit of claim 2 wherein the second switching circuit includes:

a third transistor having a first conduction terminal coupled to the second node, a second conduction terminal coupled to the first output of the frequency conversion circuit, and a control terminal coupled for receiving the second component of the local oscillator signal; and

a fourth transistor having a first conduction terminal coupled to the second node, a second conduction terminal coupled to the second output of the frequency conversion circuit, and a control terminal coupled for receiving the first component of the local oscillator signal.

4. The frequency conversion circuit of claim 3 wherein the differential transistor circuit includes:

a first current source having an output;

a fifth transistor having a first conduction terminal coupled to the first node, a second conduction terminal coupled to the output of the first current source, and a control terminal coupled for receiving a first component of the input signal; and

a sixth transistor having a first conduction terminal coupled to the second node, a second conduction terminal coupled to the output of the first current source, and a control terminal coupled for receiving a second component of the input signal.

5. The frequency conversion circuit of claim 4 further including a second current source having a first output coupled to the first node for providing the first reference current and a second output coupled to the second node for providing the second reference current.

6. The frequency conversion circuit of claim 5 wherein the second current source includes:

a seventh transistor having a first conduction terminal coupled to a power supply conductor, a second conduction terminal coupled to the first node, and a control terminal coupled for receiving a reference voltage; and

an eighth transistor having a first conduction terminal coupled to the power supply conductor, a second conduction terminal coupled to the second node, and a control terminal coupled for receiving the reference voltage.

7. The frequency conversion circuit of claim 1 wherein the current mirror circuit includes:

a first transistor having a control terminal and a first conduction terminal commonly coupled to the first output of the frequency conversion circuit, and a second conduction terminal coupled to a power supply conductor; and

a second transistor having a first conduction terminal coupled to the second output of the frequency conversion circuit, a second conduction terminal coupled to the power supply conductor, and a control terminal coupled to the control terminal of the first transistor.

8. A method of converting an input signal operating at a first frequency to an output signal operating at a second frequency, comprising:

routing a first reference current through first and second conduction paths in proportion to an input signal;

providing second and third reference currents to the first and second conduction paths, respectively;

switching a portion of the second current from the first conduction path and a portion of the third current from the second conduction path in response to a local oscillator signal to provide a differential current; and

generating the output signal by converting the differential current to a single-ended current.

9. The method of claim 8 further including:

routing the portion of the second reference current to a first output and routing the portion of the third reference current to a second output when the local oscillator signal has a first state; and

routing the portion of the second reference current to the second output and routing the portion of the third reference current to the first output when the local oscillator signal has a second state.

10. The method of claim 8, wherein a current mirror converts the differential current is to a single-ended current.

11. A wireless communication device, comprising:

a radio frequency (RF) receiver having an input coupled for receiving an RF signal; and

a frequency converter including,

(a) a differential transistor pair having first and second inputs coupled to first and second outputs of the RF receiver and first and second conduction terminals coupled to first and second nodes for receiving first and second reference currents,

(b) a first switching circuit having an input coupled to the first node, a control input coupled for receiving a local oscillator (LO) signal, and first and second outputs coupled to first and second outputs of the frequency converter, and

(c) a second switching circuit having an input coupled to the second node, a control input coupled for receiving the LO signal, and first and second outputs coupled to the first and second outputs of the frequency converter, and

(d) a differential to single-ended converter having first and second inputs coupled to the first and second outputs of the frequency converter.

12. The wireless communication device of claim 11 wherein the differential to single-ended converter includes a current mirror circuit having an input coupled to the first output of the frequency converter and an output coupled to the second output of the frequency converter for providing a single-ended output signal.

13. The wireless communication device of claim 12 wherein the current mirror circuit includes:

a first transistor having a control terminal and a first conduction terminal commonly coupled to the first output of the frequency converter, and a second conduction terminal coupled to a power supply conductor; and

a second transistor having a first conduction terminal coupled to the second output of the frequency converter, a second conduction terminal coupled to the power supply conductor, and a control terminal coupled to the control terminal of the first transistor.

14. The wireless communication device of claim 11 wherein the first switching circuit includes:

a first transistor having a first conduction terminal coupled to the first node, a second conduction terminal coupled to the first output of the frequency converter, and a control terminal coupled for receiving a first component of the LO signal; and

a second transistor having a first conduction terminal coupled to the first node, a second conduction terminal coupled to the second output of the frequency converter, and a control terminal coupled for receiving a second component of the LO signal.

15. The wireless communication device of claim 14 wherein the second switching circuit includes:

a third transistor having a first conduction terminal coupled to the second node, a second conduction terminal coupled to the first output of the frequency converter, and a control terminal coupled for receiving the second component of the LO signal; and

a fourth transistor having a first conduction terminal coupled to the second node, a second conduction terminal coupled to the second output of the frequency converter, and a control terminal coupled for receiving the first component of the LO signal.

16. The wireless communication device of claim 15 wherein the differential transistor pair includes:

a first current source having an output;

a fifth transistor having a first conduction terminal coupled to the first node, a second conduction terminal coupled to the output of the first current source, and a control terminal coupled for receiving a first component of the input signal; and

a sixth transistor having a first conduction terminal coupled to the second node, a second conduction terminal coupled to the output of the first current source, and a control terminal coupled for receiving a second component of the input signal.

17. The wireless communication device of claim 16 further including a second current source having a first output coupled to the first node for providing the first reference current and a second output coupled to the second node for providing the second reference current.

18. The wireless communication device of claim 17 wherein the second current source includes:

a seventh transistor having a first conduction terminal coupled to a power supply conductor, a second conduction terminal coupled to the first node, and a control terminal coupled for receiving a reference voltage; and

an eighth transistor having a first conduction terminal coupled to the power supply conductor, a second conduction terminal coupled to the second node, and a control terminal coupled for receiving the reference voltage.