Abstract
A current steering DAC used for digital imaging systems is presented. By analyzing the factors that deteriorate the dynamic performance of current steering DAC, this paper confirms that the performance of current switch driver and the frequency character of current sources' output impedance are the main limitations to improving spurious-free dynamic range(SFDR). In the view of this, a novel current switch driving circuit is proposed depending on the design keys of low crossing point and synchronized with the clock. In order to further improve the dynamic performance of DAC, a high output impedance current source with good frequency performance are utilized to fulfill the requirements of DAC. A quadratic curvature compensated bandgap voltage reference is also indeed to bias the current source making sure temperature stability. A 11bit 200Msps current steering DAC is implemented in GSMC 0.18μm CMOS mix-signal process. When the frequency of full range input are 20MHz, 40MHz, 60MHz and 80MHz at 200MHz sampling rate, the SFDR of DAC achieves 75.3dB, 70.8dB, 62.2dB, 60.7dB respectively.
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