Calibrating amplitude and phase imbalance and DC offset of an analog I/Q modulator in a high-frequency transmitter

• US 7,734,261 B2
• Filed: 12/09/2005
• Issued: 06/08/2010
• Est. Priority Date: 12/16/2004
• Status: Expired due to Fees

• Current Assignee: Callahan Cellular LLC (Intellectual Ventures LLC)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Bury, Andreas
• Primary Examiner(s): Nguyen, Duc
• Assistant Examiner(s): AKINYEMI, AJIBOLA A
• Application Number:
  US11/722,084
• Publication Number:
  US 20090270053A1
• Time in Patent Office: 1,642 Days
• Field of Search: 455/115.1
• US Class Current: 455/115.1
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels

Abstract

The object of the invention, which relates to a method and an arrangement for calibrating an analog I/Q modulator in a high-frequency transmitter, is to provide a method and an associated circuit arrangement by means of which a calibration of the I/Q modulator is carried out without a balancing operation and thus the complexity is minimized. According to the invention, this object is achieved, in terms of the method, in that transmission signals are produced by the I/Q modulator in three method steps in accordance with the method and said transmission signals are in each case evaluated and the results of the evaluations are stored, in that, in a fourth method step, improved compensation coefficients are calculated on the basis of the results of the previous evaluations, which improved compensation coefficients can be used for a subsequent run-through of the method, and in that the run-throughs of the method are repeated until the error of the amplitude and/or phase response of the I/Q modulator lies below a defined threshold value or a defined number of run-throughs of the method is reached.

Claims

1. A method of calibrating an analog I/Q modulator in a high-frequency transmitter, in which an input signal is weighted in an in-phase path and in a quadrature phase path by respectively a first and a second compensation coefficient prior to the I/Q modulation, and an output signal is produced, comprising:

in a first method step, providing the high-frequency transmitter

in a second method step, the first compensation coefficients C_I, C_Q (3), which affect the sideband suppression of the output signal, and the second compensation coefficients D_I, D_Q (3), which affect the carrier suppression of the output signal (12), are in each case set to a first predefined value C_I,1, C_Q,1, D_I,1 and D_Q,1, in that the input of the I/Q modulator (1) is supplied with an input signal which satisfies a rotating exponential function with the frequency f₀, a first I/Q modulator output signal (12) is produced and fed to a first evaluation and the result of the first evaluation is stored, in that,

in a third method step, the first and second compensation coefficients (3) are in each case set to a second defined value C_I,2, D_I,2 and D_Q,2 and a second I/Q modulator output signal (12) is produced, fed to a second evaluation and the result of the second evaluation is stored, in that,

in a fourth method step, the first and second compensation coefficients (3) are in each case set to a third defined value C_I,3, D_I,3 and D_Q,3 and a third I/Q modulator output signal (12) is produced, fed to a third evaluation and the result of the third evaluation is stored, in that,

in a fifth method step, improved compensation coefficients (3) which reduce at least one of an amplitude, a phase imbalance of the I/Q modulator (1) and an amplitude of the residual carrier are calculated for the first and second compensation coefficients (3) from the results stored in the second, third and fourth method steps, and

wherein the second, third, fourth and fifth method steps are repeated using these improved compensation coefficients (3) until at least one of the error of the amplitude and a phase response of the I/Q modulator (1) lies below a defined threshold value or a defined number of run-throughs of the method is reached.

2. A method as claimed in claim 1, characterized in that the first compensation coefficients (3) C_I, C_Q or the second compensation coefficients (3) D_I, D_Q have the same value for the second, third and fourth method step.

3. A method as claimed in claim 1, characterized in that, for the second method step, at least one of the first compensation coefficients (3) C_I, C_Q and the second compensation coefficients (3) D_I, D_Q are set to compensation coefficients (3) determined in a previous run-through of the method.

4. A method as claimed in claim 1, characterized in that at least one of the compensation coefficients (3) C_I, C_Q, D_I, D_Q is acted upon by at least one of a change value AC and AD prior to a subsequent method step.

5. A method as claimed in claim 1, characterized in that the input signal fed in at the input of the I/Q modulator (1), which satisfies a rotating exponential function with the frequency f₀, is produced from a partial function S_I(t)=A₀*cos(2π

f₀t+φ

₀) for the in-phase input and a partial function s_Q(t)=A₀*sin(2π

f₀+φ

₀) for the quadrature phase input.

6. A method as claimed in claim 1, characterized in that the I/Q modulator output signal (12) is subjected to power detection and thus a level indicator output signal p(t) is produced, in that the first evaluation takes place in accordance with

7. A method as claimed in claim 1, characterized in that the I/Q modulator output signal (12) is subjected to an I/Q demodulation and thus a complex baseband received signal r(t)=r_I(t)+r_Q(t) is produced, in that the first evaluation takes place in accordance with

8. A method as claimed in either of claims 6 and 7, characterized in that the integrations used in the method take place in a time-discrete manner such that sampling of the function variation takes place with a subsequent summation.

9. A method as claimed in claim 1, characterized in that the method takes place during start-up of the high-frequency transmitter, in a time-controlled manner, in the event of changing ambient conditions such as at least one of pressure and temperature and in an event of a change in operating mode of the high-frequency transmitter.