Abstract
Abstract. For software radio applications in system-on-chips, a 3rd-order current-mode Butterworth filter in 120 nm CMOS is realized. This filter is used for reconstruction purposes between a current-steering DAC and a current-mode mixer. Power can be reduced by using a current-mode architecture. The cut-off frequency of this filter is switchable between 1 MHz and 4 MHz, the current consumption is 4.5 mA at VDD=1.5 V, the inband noise density is 100 pA/√Hz and it has a dynamic range up to 65 dB.
Highlights
The integration of analog and digital functions can be achieved only when analog sections are designed with low-voltage and short-channel devices
A 3rd-order current-mode Butterworth filter was realized in a digital 120 nm CMOS technology. This filter is applied for the transmit path of a software radio system
In Otin et al (2006) a 3rd-order currentmode filter based on the Gm-C architecture in a 0.35 μm standard CMOS technology with a digital programmable cutoff frequency between 42 MHz and 215 MHz is presented which has a dynamic range of 53dB and consumes 3.7– 18.6 mW per pole
Summary
The integration of analog and digital functions can be achieved only when analog sections are designed with low-voltage and short-channel devices. As a consequence of the low supply voltage the dynamic range and the signal-tonoise ratio are reduced Annema et al (2005). It would be necessary to transform the current at the DAC output into a voltage when it is applied to a voltage-mode filter. If the signal at the filter output is applied to a current-mode mixer, the voltage must be converted into a current. The electrical power, which is used for the conversions, can be reduced, if a current-mode low-pass is used. Current-mode design can be defined as the processing of current signals in an environment where voltage signals are irrelevant in determining circuits. To obtain a high power-supply rejection ratio and to suppress common-mode noise and even-order distortions we use a fully differential topology
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