Methods and apparatus for carrier suppression in a radio modulator

• US 6,058,291 A
• Filed: 12/03/1997
• Issued: 05/02/2000
• Est. Priority Date: 12/03/1997
• Status: Expired due to Term

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Ketcham, Carl
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): SMITH, SHEILA B
• Application Number:
  US08/984,566
• Time in Patent Office: 881 Days
• Field of Search: 455/67.3, 455/46, 455/21, 455/7, 455/59, 455/109, 455/116, 455/119, 455/202, 455/293, 455/295, 455/296, 455/309, 455/312, 329/315, 329/345, 332/108, 332/119, 332/151
• US Class Current: 455/46
• CPC Class Codes: H03J 2200/28 Automatic self-alignment of a receiver
• CPC Class Codes: H04B 1/68 for wholly or partially suppressing the carrier or one side band
• CPC Class Codes: H04B 2001/0491 with frequency synthesizers, frequency converters or modulators
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0018 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

Methods and apparatus for dynamically calibrating a modulator in a radio transmitter are provided. In a preferred embodiment an In-Phase and Quadrature (I/Q) modulator in a radio modem is calibrated by means of a modulator, a digital signal processor and a power sensor. The modulator being electrically adapted to receive a local oscillator input having a carrier frequency and a substantially direct current (DC) input having an amplitude in order to produce an output having a power magnitude at the carrier frequency in a frequency defined power spectrum. The power sensor being in electrically succession to the modulator to measure the power magnitude of the output to permit the digital signal processor (DSP), electrically between the modulator and the power sensor, to compare the measured power magnitude with a minimum threshold power magnitude to determine which is greater. If the power magnitude is greater, the DSP reiteratively alters the amplitude of the DC input until the measured power magnitude of the output is less than the minimum threshold power magnitude. The minimum threshold power magnitude is preferably stored in the digital signal processor and defines a suitable power magnitude threshold at the carrier frequency beneath which the carrier frequency component will be substantially suppressed. Thereafter, the appropriate amplitude of the DC input which enabled the power magnitude of the output to fall below the minimum threshold is established in the DSP as a temporary calibration coefficient for a selected duration of time. The selected duration of time being the time from the powering on until the powering off of the radio modem or until the transmitter is selected for re-calibration by the user.

Claims

1. In a frequency defined power spectrum, a method for suppressing a carrier frequency component in a radio transmitter, the steps comprising:

combining a substantially direct current (DC) input having an amplitude with a local oscillator input having a carrier frequency in a modulator to obtain an output having a power magnitude at said carrier frequency;

defining a minimum threshold power magnitude at said carrier frequency suitable for use in said radio transmitter that substantially suppresses said carrier frequency component when said power magnitude is less than said minimum threshold power magnitude;

altering by an altered amplitude said amplitude of said DC input until said power magnitude of said output is less than said minimum threshold power magnitude;

reiteratively performing said step of altering said amplitude of said DC input until said power magnitude achieves a local minimum power magnitude; and

thereafter, establishing said altered amplitude of said DC input as a calibration correction coefficient.

2. A method according to claim 1, wherein said step of reiteratively performing said step of altering said amplitude of said DC input is performed in about 50 reiterative steps.

3. A method according to claim 2, wherein said step of altering said amplitude of said DC input is performed in increments of less than about 1% of a previous amplitude level.

4. In a frequency defined power spectrum, a method for calibrating a modulator having at least two channels to substantially suppress a carrier frequency component in a radio modem, the steps comprising:

in a first channel,

a) combining a substantially direct current (DC) input having an amplitude with a local oscillator input having a carrier frequency in said modulator to obtain an output having a power magnitude at said carrier frequency;

b) defining a minimum threshold power magnitude at said carrier frequency suitable for use in said radio modem that substantially suppresses said carrier frequency component when said power magnitude is less than said minimum threshold power magnitude;

c) altering by an altered amplitude said amplitude of said DC input until said power magnitude of said output is less than said minimum threshold power magnitude, further comprising the steps of;

c1) sensing said power magnitude of said output with a power sensor electrically succeeding a transmitter stage of said modem;

c2) communicating said sensed power magnitude to a digital signal processor to allow adjustment of said amplitude of said DC input to one of a higher and lower value to provide another output having an altered power magnitude at said carrier frequency; and

c3) repeating said steps c1) and c2) until said another power magnitude is less than said minimum threshold power magnitude;

d) thereafter, establishing said altered amplitude of said DC input as a calibration correction coefficient; and

e) repeating said steps a) through d) for a second channel.

5. In a frequency defined power spectrum, a method for calibrating a modulator having at least two channels to substantially suppress a carrier frequency component in a radio modem, the steps comprising:

in a first channel,

a) providing a statically calibrated zero representing the absence of information to a digital to analog convertor (DAC), said DAC electrically preceding said modulator, to enable input of said DC input to said modulator;

b) combining a substantially direct current (DC) input having an amplitude with a local oscillator input having a carrier frequency in said modulator to obtain an output having a power magnitude at said carrier frequency;

c) defining a minimum threshold power magnitude at said carrier frequency suitable for use in said radio modem that substantially suppresses said carrier frequency component when said power magnitude is less than said minimum threshold power magnitude;

d) altering by an altered amplitude said amplitude of said DC input until said power magnitude of said output is less than said minimum threshold power magnitude;

e) thereafter, establishing said altered amplitude of said DC input as a calibration correction coefficient; and

f) repeating said steps a) through e) for a second channel.

6. In a frequency defined power spectrum, a method for calibrating a modulator having at least two channels to substantially suppress a carrier frequency component in a radio modem, the steps comprising:

in a first channel,

a) combining a substantially direct current (DC) input having an amplitude with a local oscillator input having a carrier frequency in said modulator to obtain an output having a power magnitude at said carrier frequency;

b) defining a minimum threshold power magnitude at said carrier frequency suitable for use in said radio modem that substantially suppresses said carrier frequency component when said power magnitude is less than said minimum threshold power magnitude;

c) altering by an altered amplitude said amplitude of said DC input until said power magnitude of said output is less than said minimum threshold power magnitude;

d) thereafter, establishing said altered amplitude of said DC input as a calibration correction coefficient, said step further comprising the step of temporarily storing said calibration correction coefficient in a digital signal processor for a selected time duration, thereafter when said modem is used to transmit information during said selected time duration, said digital signal processor employs said calibration correction coefficient to set a selected power level for an information signal input to the modulator thereby substantially suppressing said carrier frequency component; and

e) repeating said steps a) through d) for a second channel.

7. A radio modem being capable of dynamically calibrating a modulator therein to substantially suppress a carrier frequency component in a frequency defined power spectrum, comprising:

a modulator electrically adapted to receive a local oscillator input having a carrier frequency and a substantially direct current (DC) input having an amplitude to produce an output having a power magnitude at said carrier frequency in said frequency defined power spectrum; and

a power sensor electrically succeeding said modulator for measuring said power magnitude of said output to enable a digital signal processor electrically between said modulator and said power sensor to compare said measured power magnitude with a minimum threshold power magnitude and when said power magnitude is above said minimum threshold reiteratively alter said amplitude of said DC input until said measured power magnitude is less than said minimum threshold power magnitude, said minimum threshold power magnitude being stored in said digital signal processor to define a suitable power magnitude threshold at said carrier frequency below which said carrier frequency component will be substantially suppressed.

8. A radio modem according to claim 7, further comprising a transmitter stage electrically preceding said power sensor for amplifying said output of said modulator in preparation for transmitting information across a communication channel.

9. A radio modem according to claim 7, wherein said modulator is a two channel modulator for facilitating numerous modulation schemes therein, said two channels being an in-phase channel and a quadrature channel.

10. A radio modem according to claim 7, further comprising a digital to analog convertor (DAC) in electrical succession to said digital signal processor, said DAC being capable of receiving a statically calibrated zero representing the absence of information to produce said substantial DC input for said modulator.