| 摘要 |
A system for automatically calibrating a main digital to analog converter (DAC) includes first and second adjustment DAC's, an offset DAC, a difference amplifier, an analog to digital converter (ADC), a microprocessor, and an analog switch. To calibrate the offset of the main DAC, the microprocessor causes "zeros" to be applied to the digital inputs of the main DAC and the offset DAC. The output of the offset DAC is coupled to an input of the difference amplifier. The microprocessor causes a ground voltage to be applied to the second input of the difference amplifier via the analog switch. The output of the difference amplifier is inputted to the ADC, which produces a first word. The first word is stored by the microprocessor. The analog switch is activated to apply the analog output voltage of the main DAC to the second input of the difference amplifier. The ADC produces a second word which is compared to the first word. The microprocessor computes a first correction word which is transmitted to the first adjustment DAC. The first adjustment DAC produces a corresponding analog signal which is applied to a first correction input of the main DAC, causing the analog output voltage to be adjusted toward the ground voltage. To calibrate the linearity of the main DAC, the microprocessor causes the analog voltage corresponding to the fourth most significant bit to be converted to a third digital word by means of the ADC, and then causes the analog output voltage corresponding to the sum of the less significant bits to be converted to a fourth word by means of the ADC. The difference between the third and fourth words is used by the microprocessor to compute a second correction code. The second correction code is converted to a second analog correction signal by the second DAC, causing the third analog output voltage to differ from the second analog output voltage by an amount corresponding to one least significant bit. |
