Flexible baseband Low-Pass Filter and Variable Gain Amplifier for Software Defined Radio Front End

Abstract

Analog blocks intended for software defined radio have to be targeted to multi-standard operation trying to guarantee at any time a near optimal power-performance trade-off. A novel approach to design a digitally programmable low pass filter (LPF) and variable gain amplifier (VGA) is here defined. These baseband blocks are driven by a Network-on-Chip that is able to set performances like cut-off frequency, selectivity, noise, and gain conveniently adapting the power consumption. The LPF provides a wide frequency tuning range between 0.35MHz and 23.5MHz with an adaptive integrated noise level between 85µVrms and 163µVrms and a current consumption that moves from 1.5mA to 18mA. The VGA is made up of 2 cascaded gain stages and provides a gain range from 0dB to 39dB. The prototype was realized in 0.13µm CMOS technology. Measurements results validate the adopted approach.

Baseband Analog Circuits for Software Defined Radio

“…RX channel filtering is provided by a cascade of Active-g m -RC biquadratic cells that can independently set its order and R and C values, and therefore provides a channel bandwidth continuously programmable between 350 kHz and 23 MHz, second-, fourth-, or sixth-order transfer function, and an input referred noise level perfectly proportional to the power consumption (Giannini et al, 2006b). Also the variable gain amplifier can program not only its gain in 3 dB steps, but also its bandwidth and noise level.…”

“…An extremely flexible solution is proposed in (Giannini et al, 2006b) that exploits a Switchable Op-Amp (SOA), shown in Figure 4.4. The Switchable Op-Amp (SOA) represents the basic switchable unit of the Flexible Op-Amp (FLOA), shown in Figure 4.5, which is made up of parallel connections of SOA in a binary-scaled array.…”

A Low Power Reconfigurable Analog Baseband Block for Software Defined Radio

“…The latter scheme requires less area as it shares the capacitor for various applications. Continuous time filter using switchable operational amplifier and capacitor arrays is proposed in [6] to achieve flexible trade off between power and bandwidth. A G m -C Low-pass Filter for zero-IF Mobile Applications with a tuning range of 100 KHz to 2.11 MHz is achieved in [7] using Si-Ge process.…”

“…The growing popularity and importance of mobile communication, and the evolution of different standards for voice and data are pushing the research towards the implementation of fully integrated multi standard transceivers [1][2][3][4][5][6]. Such transceivers should switch seamlessly among different standards in order to achieve the so-called "global roaming" for both voice and data applications.…”

Receiver Architectures for Software-defined Radios in Mobile Terminals: the Path to Cognitive Radios

“…Reconfigurablity in the baseband section is achieved by again employing heavy digital control on a lowpass filter that is able to change its component values according to the instantaneous requirements and hence allows a large trade-off range in bandwidth, noise level and power consumption [3]. This programmable analog lowpass filter at baseband is key to suppressing the level of nearby interferers and reducing the ADC dynamic range requirement.…”