A 1-V CMOS current steering digital to analog converter with enhanced static and dynamic linearity is presented. The 14-bit static linearity is achieved by a novel background analog self calibration technique which is suitable for low voltage applications and does not require error measurement and correction circuits. To improve dynamic linearity at high frequencies, a new low power track/attenuate output stage is used at the DAC output. Integral and differential nonlinearities of the proposed DAC corresponding to 14-bit specification are less than 0.35LSB and 0.25LSB, respectively. The DAC is functional up to 400MS/s with SFDR better than 71dB in the Nyquist band. The circuit has been designed and simulated in a standard 0.18u CMOS technology.Index Terms -digital to analog converter (DAC), self calibration, dynamic nonlinearities, track/attenuate output stage.
A 3.6 order, 1.1 MHq lowpass butterworth Gm-c filter has been combined with a low noise Variable Gain Amplifier to form the Variable Gain Filter (VGF). In this VGF an improved transconductor is used and B new method is used IO adjust the transeonduelance gain for tuning application. A continuous variable gain current-to-current converter is used to tune the transeonduetor value. The THD of the VGF i s -85 dB for I Vpp. input signal and -50 dB for 3 V,,a input signal. VGF gain can be varied from 0 to 31 dB with 1 dB wristion steps. Input referred noise is 20 nV/\IHz for maximum gain. All the circuits arc designed based on a 0.25 pm CMOS process technology.
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