Balanced power amplifier for low power radio communications

• US 6,711,392 B1
• Filed: 06/30/2000
• Issued: 03/23/2004
• Est. Priority Date: 06/30/2000
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Gillis, John D.
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): RAMPURIA, SHARAD K
• Application Number:
  US09/609,066
• Time in Patent Office: 1,362 Days
• Field of Search: 455/91, 455/127, 455/115, 455/116, 455/552, 330/129, 330/124.R
• US Class Current: 455/253.2
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 2203/7206 the gated amplifier being switched on or off by a switch in the bias circuit of the amplifier controlling a bias voltage in the amplifier
• CPC Class Codes: H03F 2203/7215 the gated amplifier being switched on or off by a switch at the input of the amplifier
• CPC Class Codes: H03F 2203/7221 the gated amplifier being switched on or off by a switch at the output of the amplifier
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H03F 3/602 Combinations of several amplifiers
• CPC Class Codes: H03F 3/72 Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes
• CPC Class Codes: H04B 2001/045 with means for improving efficiency

Abstract

A balanced power amplifier for radio frequencies. The power amplifier may be switched from operating in a saturation mode, so that AMPS-type radio telephone signals may be optimally amplified, to a linear mode so that CDMA signals may be amplified. A directional coupler splits an input signal into quadrature signal components which are supplied to the input of a pair of dual mode power amplifiers. The output signals from the dual mode amplifiers are recombined in a directional coupler. The directional coupler effectively applies all of the output power to an antenna connected to one of the coupler ports, and effectively isolates the output stages of the amplifiers from any reflected power generated by the antenna.

Claims

1. A balanced power amplifier having a switched load comprising:

a first directional coupler connected to receive on one port thereof a signal for amplification;

a first power amplifier having a switched load which selects a high linearity mode or a saturation mode of operation connected to receive a signal for amplification from a second port of said first directional coupler;

a second power amplifier having a switched load which selects a high linearity mode or a saturation mode of operation, connected to receive a signal for amplification from a third port of said first directional coupler;

a second directional coupler having first and second ports connected to receive signals from said first and second power amplifiers, whereby a combined output signal is produced at a third port of said coupler.

2. The balanced power amplifier according to claim 1 wherein an antenna is connected to receive said output signal, said directional coupler having a load impedance connected to a fourth port of said coupler whereby reflected power from said antenna is directed to said load impedance.

3. The balanced amplifier according to claim 1 wherein each of said power amplifiers include an electronic switch connected in series with an impedance element, said impedance element forming a load impedance across said amplifier which increases or decreases said amplifier load impedance.

4. The balanced amplifier according to claim 3 further comprising a digital interface connected to said electronic switch.

5. The balanced amplifier according to claim 1 further comprising a load impedance connected to a fourth port of said first directional coupler for absorbing reflected power from said first and second amplifiers.

6. The balanced amplifier according to claim 3 wherein said impedance element is a capacitor.

7. The balanced amplifier according to claim 3 wherein said impedance element shifts the amplifier load line to produce a linear output signal.

8. A method for reducing the effects of antenna VSWR on a switched power amplifier comprising:

dividing a signal to be amplified into first and second quadrature related signals;

amplifying said first quadrature related signal in a first amplifier which selectively operates in a saturation mode and a linear mode;

amplifying said second quadrature related signal in a second amplifier which selectively operates in a saturation mode and a linear mode; and

combining said amplified quadrature related signals in a directional coupler connected to a load impedance.

9. The method according to claim 8 wherein:

the output impedance of each of said first and second amplifiers is changed to select said saturated mode or said linear mode of operation.

10. The method according to claim 8 wherein said load impedance is an antenna of a portable telephone.

11. The method according to claim 8 further comprising selecting said linear mode when said signal is a CDMA based signal.

12. The method according to claim 8 further comprising selecting said saturation mode when said signal is an AMP-based signal.