DE102005011916A1 - Digital to analog converter DC offset calibration method, involves calibrating converter based on DC compensation value that is determined based on set of values and measurement values, without using preset calibration parameter - Google Patents

Abstract

The method involves applying a set of values to a digital to analog converter (DAC) to generate respective measurement values. A DC compensation value is determined according to the set of values and measurement values without using predetermined calibration parameter. The digital to analog converter is calibrated based on the DC compensation value by adjusting digital input values of the DAC. An independent claim is also included for an apparatus for calibrating the digital to analog converter (DAC).

Description

These The invention relates to a method and a device for Calibration of the DC offset of a digital / analog converter according to the preambles of claims 1 and 9.

Regardless of the type of modulation scheme used in a communication system, a digital-to-analog converter is generally used for transmission to convert a digital modulated signal to an analog signal. Due to ambient temperature changes or manufacturing process variations, most existing digital to analog converters can not be considered ideal components. A non-ideal effect exhibited by a real digital-to-analog converter is called a "DC offset effect," which causes the conversion curve of the digital-to-analog converter to become defective. In particular, the DC offset effect causes the conversion curve of the digital / analog converter to deviate from the coordinate origin. In other words, even with a digital input value x of the real digital / analog converter, the analog output value y of the real digital / analog converter is a value deviating from zero. The non-zero value is referred to as the DC offset value y _{D of} the real digital-to-analog converter. The DC offset value y _D disturbs the signal transmission quality and degrades the performance of the communication system using the real digital-to-analog converter. For some types of communication systems that require high signal transmission quality, the DC offset effect is a problem that must be solved.

Around the problems caused by the DC offset effect To avoid, in the method of the prior art a compensation regarding of the digital input signal of the digital / analog converter to to eliminate the DC offset effect. In particular, tests The prior art method many sample chips to an average characteristic value of the digital / analog converter in the sample chips to determine. Subsequently the prior art method sets the average characteristic value as a predetermined calibration parameter in every chip. Each chip uses the only predetermined calibration parameter, to compensate for its DC offset effect of the digital-to-analog converter.

however have digital / analog converters on different chips sometimes different DC offset values. It is even too for one single digital / analog converter possible that the digital / analog converter has different DC offset values at different times. As a result, it is possible the average characteristic value is not a suitable calibration parameter for all Chips is. The use of possibly inaccurate average characteristic value than the predetermined one Calibration parameter can cause the DC offset effect of the digital / analog converter is not exactly eliminated.

This Considered This invention aims to provide a method of calibration the DC offset of a digital-to-analog converter, that does not use a predetermined calibration parameter and consequently accurately eliminates the DC offset of the digital-to-analog converter.

This is achieved by a method and apparatus for calibrating the DC offset of a digital / analog converter according to claims 1 and 9 reached. The dependent claims refer to corresponding developments and improvements.

As recognized more clearly from the following detailed description eliminates the claimed method of calibration the DC offset of a digital / analog converter the DC offset effect a digital-to-analog converter without a predetermined calibration parameter to use; it follows that no erroneous result is generated is, and that the DC offset effect of a digital / analog converter is accurately eliminated.

in the The invention will now be described with reference to the accompanying drawings further exemplified. Show it:

1 a block diagram showing how components are connected when the method is carried out according to this invention, and

2 a flowchart illustrating a method for calibrating the DC offset of a digital / analog converter according to this invention.

To avoid the problem of inaccurate calibration caused by the use of predetermined parameters, this invention calibrates the DC offset effect of a digital-to-analog converter without the use of a predetermined parameter. In particular, this invention uses an interpolation method to determine the DC offset value of the digital-to-analog converter and uses the well-determined DC offset value to calibrate the digital-to-analog converter. Since no predetermined parameter is required, no tests with many sample chips need to be performed in accordance with the invention to determine the required parameters (such as the previously indicated calibration parameter ρ _ZX ). In addition, it follows that a predetermined parameter does not have to be pre-stored in every system; This saves further storage space.

To the DC offset effect of a digital / analog converter 220 To calibrate, according to this invention, the output terminal of the digital / analog converter 220 to the input terminal of an analog-to-digital converter 230 connected and the output terminal of the analog / digital converter 230 comes with a calculation module 240 connected. The interconnections between these three components are in the 1 shown. In the 1 can the digital / analog converter 220 and the analog to digital converter 230 a digital-to-analog converter in the transmitting branch of a transmitter and an analog-to-digital converter in the receiving branch of a transmitter, but they are not limited thereto.

2 FIG. 12 shows a flowchart of a method for calibrating the DC offset of a digital-to-analog converter according to an embodiment of this invention. In the 2 shown steps are as follows. First, in one step 310 a first value x _{1 is applied} to the digital / analog converter 220 and the output value of the analog / digital converter 230 is measured as a first measured value z ₁ . After that, in one step 320 a second value x ₂ to the digital / analog converter 220 applied and the output value of the analog / digital converter 230 is measured as a second measured value z ₂ . By means of these two steps, the following equations (1) and (2) are obtained: z 1 = ρ ZX · (X 1 - x C ) + z D (1); z 2 = ρ ZX · (X 2 - x C ) + z D (2);

In equations (1) and (2) two values remain unknown, namely ρ _ZX and x _c (where x _{c is} the DC offset value of the digital / analog converter 220 is). The two unknown values can be determined by the two equations. Consequently, the calculation module 240 in step 330 without using a predetermined calibration parameter, determine the DC compensation value x _c corresponding to the first value x ₁ , the second value x ₂ , the first measured value z _1, and the second measured value z ₂ in a variety of manners. In step 330 is a first way that the calculation module 240 determines the DC compensation value x _c according to the following equation (3): x c = [(z 2 - z D ) .X 1 - (z 1 - z D ) .X 2 ] / (Z 2 - z 1 ) (3).

A second possibility of the step 330 is that the calculation module 240 First, determine the slope value ρ _ZX and then substitute the determined slope value ρ _ZX into the equation (1), the equation (2), or another equation composed of other input / output values to determine the DC compensation value x _c . The equations used in the second solution are as follows: ρ ZX = (z 2 - z 1 ) / (X 2 - x 1 ) (4) x D = x 1 - [(z 1 - z D ) / Ρ ZX ] (5).

Since no potentially inaccurate calibration parameter is used, that is from the calculation module 240 certain DC compensation value x _{c is} a value representing the DC offset effect of the digital / analog converter 220 correctly represented. Finally, in step 340 After each of the components has been switched back to its original position in the system, a compensation module (such as an adder) connected to the input terminal of the digital-to-analog converter 220 connected, used to the digital / analog converter 220 according to the determined DC Kompensatioswerts x _c to calibrate. In particular, the DC compensation value x _c is subtracted from each digital value before the digital value is sent to the digital / analog converter 220 is created. The DC offset effect of the digital-to-analog converter 220 is thereby eliminated.

In summary, this invention discloses a method and apparatus for calibrating a DC offset of a digital to analog converter 220 , The disclosed method comprises the following steps. First, a first value and a second value are applied to the digital-to-analog converter 220 created to generate a first measured value and a second measured value. Subsequently, a DC compensation value corresponding to the first value, the second value, the first measurement value and the second measurement value is determined without using a predetermined parameter. The DC compensation value is used to drive the Digital / Ana log converter 220 to calibrate.

in the Unlike the conventional one Method, this invention has some advantages. An advantage is that no predetermined calibration parameter is used, whereby this invention does not require additional storage space to store predetermined calibration parameters. Another advantage is that the DC offset value for each individual chip is accurate is determined and subsequently a digital compensation is performed, reducing the DC offset effect is eliminated correctly. Even if environmental parameters cause that the properties of a single chip can change This invention still easily adds the DC offset effect of the single chip.

Claims (16)

A method for calibrating the DC offset for calibration of a digital / analog converter ( 220 ), with the steps: applying a first value to the digital / analog converter ( 220 ) to generate a first measured value; Applying a second value to the digital / analogue converter ( 220 ) to generate a second reading; characterized by the steps of: determining a DC compensation value corresponding to the first value, the second value, the first measurement value, and the second measurement value without the use of a predetermined calibration parameter; and calibrating the digital / analog converter ( 220 ) with the DC compensation value. The method according to claim 1, characterized in that the step of calibrating the digital / analog converter ( 220 ) comprises: using the DC compensation value to obtain digital input values of the digital-to-analog converter ( 220 ) before the digital input values to the digital / analog converter ( 220 ). The method according to claim 1 or 2, characterized in that the first measured value and the second measured value in each case to analog output signals of the digital / analog converter ( 220 ) when the first value and the second value are applied to the digital / analog converter ( 220 ). The method of any of claims 1 to 3, further characterized by the step of: connecting an output terminal of the digital to analog converter ( 220 ) with an input terminal of an analog / digital converter ( 230 ); wherein the first measured value and the second measured value are respectively connected to digital output values of the analog / digital converter ( 230 ) when the first value and the second value are applied to the digital / analog converter ( 220 ). The method according to claim 4, characterized in that the DC compensation value is determined according to the following equation: x c = [(z 2 - z D ) .X 1 - (z 1 - z D ) .X 2 ] / (Z 2 - z 1 ) where z _{D is} a DC offset value of the analog / digital converter ( 230 ), x _{c is} the DC compensation value, x _{1 is} the first value, x _{2 is} the second value, z _{1 is} the first measured value, and z _{2 is} the second measured value. The method according to one of the claims 1 to 4, characterized in that the step of determining the DC compensation value further comprises: Determine a slope value accordingly the first value, the second value, the first measured value and the second measured value; and Determining the DC compensation value according to the slope value, the first value and the first one Reading. The method according to claim 6, characterized in that the slope value and the DC compensation value are determined according to the following equations: ρ ZX = (z 2 - z 1 ) / (X 2 - x 1 ); and x C = x 1 - [(z 1 - z D ) / Ρ ZX ] where z _{D is} a DC offset value of the analog / digital converter ( 230 ), ρ _{ZX is} the slope value, x _{c is} the DC compensation value, x _{1 is} the first value, x _{2 is} the second value, z _{1 is} the first measured value, and z _{2 is} the second measured value. The method according to one of the claims 1 to 7, characterized in that the method in a transmitter or transceiver is used. A device for calibrating a DC offset effect of a digital-to-analog converter, comprising: a digital-to-analog converter ( 220 ); characterized by a calculation module ( 240 ) electrically connected to the digital / analog converter ( 220 ) is connected to a DC compensation value corresponding to a first value, a second value, a first measured value and a second measured value to determine without using a predetermined calibration parameter; and wherein the device uses the DC compensation value to calibrate the digital-to-analog converter. The device according to claim 9, characterized in that the device uses the DC compensation value to transmit to the digital / analogue converter ( 220 ) to adjust the digital values to be created. The device according to claim 9 or 10, characterized in that the first measured value and the second measured value respectively to analog output signals of the digital / analog converter ( 220 ) when the first value and the second value are applied to the digital / analog converter ( 220 ). The apparatus of any one of claims 9 to 11, further characterized by: an analog to digital converter ( 230 ) is electrically connected to an output terminal of the digital / analog converter ( 220 ) and an electrical connection to the calculation module ( 240 ) connected output terminal; wherein the first measured value and the second measured value are respectively connected to digital output signals of the analog / digital converter ( 230 ) when the first value and the second value are applied to the digital / analog converter ( 220 ). The device according to claim 12, characterized in that the calculation module ( 240 ) determines the DC compensation value according to the following equation: x c = [(z 2 - z D ) .X 1 - (z 1 - z D ) .X 2 ] / (Z 2 - z 1 ) where z _{D is} a DC offset value of the analog / digital converter ( 230 ), x _{c is} the DC compensation value, x _{1 is} the first value, x _{2 is} the second value, z _{1 is} the first measured value, and z _{2 is} the second measured value. The device according to one of the claims 1 to 12, characterized in that the calculation module ( 240 ) determines a slope value corresponding to the first value, the second value, the first measurement value, and the second measurement value; and the calculation module ( 240 ) further determines the DC compensation value according to the slope value, the first value, and the first measurement value. The device according to claim 14, characterized in that the calculation module ( 240 ) determines the slope value and the DC compensation value according to the following equations: ρ ZX = (z 2 - z 1 ) / (X 2 - x 1 ); and x C = x 1 - [(z 1 - z D ) / Ρ ZX ]; where z _{D is} a DC offset value of the analog / digital converter ( 230 ), ρ _{ZX is} the slope value, x _{C is} the DC compensation value, x _{1 is} the first value, x _{2 is} the second value, z _{1 is} the first measured value, and z _{2 is} the second measured value. The device according to one of the claims 9 to 15, characterized in that the device in a transmitter or a transceiver is installed.