Smart amplifier for time division duplex wireless applications

• US 6,681,100 B1
• Filed: 03/14/2000
• Issued: 01/20/2004
• Est. Priority Date: 03/15/1999
• Status: Expired due to Fees

• Current Assignee: Teletronics International Incorporated
• Original Assignee: Teletronics International Incorporated
• Inventors: Ge, David
• Primary Examiner(s): Gary, Erika
• Application Number:
  US09/524,745
• Time in Patent Office: 1,407 Days
• Field of Search: 455/134, 455/13.4, 455/69, 455/38.2, 455/73, 455/127.1, 455/127.2, 455/522, 455/78, 455/83, 455/115.1, 455/115.3, 375/99, 325/402, 381/321
• US Class Current: 455/78
• 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 1/3877 Arrangements for enabling portable transceivers to be used in a fixed position, e.g. cradles or boosters
• CPC Class Codes: H04B 1/48 in circuits for connecting transmitter and receiver to a common transmission path, e.g. by energy of transmitter H04B1/46 takes precedence
• CPC Class Codes: H04B 1/56 with provision for simultaneous communication in two directions

Abstract

A bi-directional antenna-mount amplifier particularly suited to be compatible with a broad range of advanced spread spectrum TDD wireless applications relying on either direct sequence or frequency hopping, at a wide range of frequencies, and which allows the radio device sharing of an associated antenna in different time intervals, where signal distortion is minimized due to operation of the amplifier which is governed by an equation and associated gain control circuits to maintain constant output power and prevent transmit signal saturation.

Claims

1. In combination:

an RF antenna;

a bi-directional RF amplifier module;

a DC injector;

a bi-directional cable; and

an RF modem,

said RF amplifier module including

an RF input power sensor,

an RF power level detector for determining if the RF power level on said bi-directional cable is below a select threshold,

a transmit gain control circuit responsive to the RF power level on said bi-directional cable,

a first switch, and

a second switch,

said DC injector being connected to said RF amplifier module by said bi-directional cable, said cable being capable of carrying a bi-directional RF signal and DC power, where the transmit gain control circuit maintains substantially constant output power in a transmit mode, and the amplifier module switches from the transmit mode to a receive mode when the RF power is below said select threshold.

2. The combination of claim 1 where the RF input power level detector comprises a voltage comparator connected to a threshold signal source set at a select threshold and a control switch for switching between transmit and receive modes, said voltage comparator being connected to a subtractor which is also connected to a voltage reference source.

3. The combination of claim 2 where said transmit gain control circuit forms a feedback loop comprising a variable attenuator with an input from said subtractor, said variable attenuator being connected to a transmit amplifier which is connected to said first switch, said first switch being switchably connected to said antenna and connected to a bandpass filter, said bandpass filter being connected to a low noise amplifier that is connected to said second switch, said second switch including an output to said bi-directional cable which switchably connects said bi-directional cable and said variable attenuator.

4. The combination of claim 1 further comprising a power circuit connected to said second switch output.

5. The combination of claim 4 further comprising a power supply connected to said DC injector.

6. The combination of claim 1 where the transmit gain control circuit operates to maintain substantially constant output power to minimize signal distortion of said RF amplifier operating at a frequency band selected from the group of 900 MHz, 2.4 GHz, and 5.8 GHz.

7. The combination of claim 6 where the transmit gain control circuit operates according to the equation

8. The combination of claim 1 further comprising a lighting strike protection circuitry.

9. The combination of claim 1 further comprising a DC surge protection circuitry.

10. The method of maintaining substantially constant output power of the amplifier in a combination according to claim 1, comprising the step of operating the amplifier according to the equation

11. The combination of claim 1 wherein the transmit gain control circuit is responsive to the RF input power sensor.

12. A circuit for a system having a signal source, an antenna, and a bi-directional cable coupled to the signal source and the antenna, the circuit comprising:

a variable gain amplifier comprising a gain control module and a transmitting amplifier having a first input for coupling to the bi-directional cable, an output for coupling to the antenna, and a second input, wherein the variable gain amplifier amplifies an RF signal on the first input to produce an amplified signal on the output, and varies gain responsive to a signal on the second input; and

a power detection module having an input for coupling to the bi-directional cable, the power detection module having an output coupled to the second input of the amplifier,

wherein the power detection module is responsive to a power level on the bi-directional cable.

13. The circuit of claim 12 further including a switch coupled between the variable gain amplifier output and the antenna, the switch having a control input, and a voltage comparator having an output coupled to the control input of the switch.

14. The circuit of claim 12 wherein the variable gain amplifier includes a variable attenuator.

15. The circuit of claim 12 wherein the variable gain amplifier varies gain to maintain substantially constant output power.

16. The circuit of claim 15 wherein the variable gain amplifier maintains output power in accordance with

17. The circuit of claim 12 further comprising circuitry to protect the variable gain amplifier from lightning.

18. The circuit of claim 12 wherein the signal source includes an RF modem.

19. The circuit of claim 12 further including

a signal path that passes signals between the signal source and the bi-directional cable;

and

a power source that sends power to the amplifier, via the signal path.