Radio frequency device with fast charging of an input capacitance

• US 6,438,364 B1
• Filed: 06/06/2000
• Issued: 08/20/2002
• Est. Priority Date: 06/06/2000
• Status: Expired due to Term

• Current Assignee: Callahan Cellular LLC (Intellectual Ventures LLC)
• Original Assignee: Philips Electronics North America Corporation (Koninklijke Philips N.V.)
• Inventors: Waite, Helen Margaret
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Lee, John J.
• Application Number:
  US09/588,386
• Time in Patent Office: 805 Days
• Field of Search: 455/323, 455/326, 455/330, 455/333, 455/355, 455/318, 357/355, 357/357, 357/359, 320/166, 320/167
• US Class Current: 455/323
• CPC Class Codes: H03F 1/22 by use of cascode coupling, i.e. earthed cathode or emitter stage followed by earthed grid or base stage respectively
• CPC Class Codes: H03F 1/305 in case of switching on or off of a power supply
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 2200/372 Noise reduction and elimination in amplifier
• CPC Class Codes: H03F 2200/391 the output circuit of an amplifying stage comprising an LC-network
• CPC Class Codes: H03F 2200/492 A coil being added in the source circuit of a transistor amplifier stage as degenerating element
• CPC Class Codes: H03F 2203/45506 the CSC comprising only one switch
• CPC Class Codes: H03F 3/72 Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal

Abstract

A radio frequency device has an input transistor from which a capacitance is seen, and a fast charging circuit for charging the capacitance. The input transistor receives a radio frequency signal. The capacitance is quickly charged when the device is switched from off to on and/or from low gain to high gain, thereby reducing the switching-on time of the device.

Claims

1. A radio frequency device comprising:

an input transistor comprising an input electrode from which a capacitance is seen, said input transistor being switchable between an on-mode and an off-mode, and said input electrode receiving a radio frequency signal; and

a charging circuit for charging said capacitance when said input transistor is switched from said off-mode to said on-mode, said charging circuit comprising;

a differential amplifier with differential inputs and a current sensing resister connected across the differential inputs to detect a quantity of current flowing across the input transistor and to cause said charging to automatically cease if said quantity has changed from a first value to a second value, said second value occurring when said capacitance is fully charged;

a first current mirror for mirroring a first output current at a first output of said differential amplifier;

a second current mirror for mirroring a second output current of said differential amplifier;

a third current mirror that is coupled to said first and second current mirrors, said second current mirror providing a charging current upon initiation of said charging, and said third mirror fully sinking said charging current if said quantity has adopted said second value; and

a charging transistor of which an input electrode receives said charging current, and an output electrode provides a current amplified charging current, said current amplified charging current charging said capacitance.

2. A radio frequency device as claimed in claim 1, further comprising gain mode switching means for switching said radio frequency device into at least a first gain mode and a second gain mode, in said first gain mode said radio frequency device having a lower gain than in said second gain mode, said input transistor being coupled to said gain mode switching means, and said gain mode switching means switching said radio frequency device from said first into said second gain mode when said input transistor is switched from said off-mode to said on-mode.

3. A radio frequency device as claimed in claim 1, wherein said charging circuit comprises an enable input for enabling said charging circuit.

4. A radio frequency device as claimed in claim 3, wherein said charging circuit comprises a transistor switch coupled to said input electrode of said charging transistor, said transistor switch being controlled to switch off said charging transistor after said capacitance is fully charged.

5. A radio frequency device as claimed in claim 1, said radio frequency device being a low noise amplifier, said radio frequency device further comprising a cascode transistor configured into a cascade circuit configuration with said input transistor.

6. A radio frequency device as claimed in claim 1, said radio frequency device being a mixer, said radio device further comprising a differential pair to inputs of which local oscillator signals are provided, main current paths of said differential pair being configured between a intermediate frequency load and an output electrode of said input transistor.

7. A radio frequency device as claimed in claim 6, wherein said charging circuit is configured to sense a quantity at a node formed by said differential pair and said input transistor.

8. A radio frequency device as claimed in claim 7, wherein said radio frequency device comprises a current sensing resistor coupled to said node.