A CMOS variable gain amplifier (VGA) based on a novel linear and tunable triode transconductor is presented. The proposed transconductor employs local negative feedback for linearisation controlling the drain voltage of the input transistors biased in the triode region. The new design is able to operate at low supply voltage and the stability is guaranteed. The transconductor features a 47.75 dB dc gain and a 4.23 MHz unity gain frequency with a power consumption of only 91 µA. To show the feasibility of the proposed transconductor, a VGA has been fabricated. Measurement results for a 0.13 µm CMOS design show a −3 dB bandwidth above 2.8 MHz and a third-order harmonic distortion at 500 kHz below −46 dB over the whole gain range. The VGA exhibits a maximum power consumption of only 395 µW from a single 1.2 V supply.

A Gm-C third-order Chebyshev low-pass filter with a novel switched capacitor frequency tuning technique for a zero-IF Bluetooth receiver has been designed. The frequency tuning scheme is simpler and has more relaxed specifications than conventional ones. Furthermore, a highly linear pseudo-differential transconductor with a compact feedback loop able to operate with low supply voltage has been used. This control loop holds the input transistors in triode region and provides high output resistance, keeping high linearity in a wide range of transconductance. The filter bandwidth is 0.5 MHz and the overall scheme consumes 1.1 mA from a 1.8-V supply. The measured third-order intermodulation (IM3) distortion of the filter for a 1 Vpp two-tone signal centered at 300 kHz is 65 dB.

A third-order Gm-C Chebyshev low-pass filter with high linearity and automatic frequency programmability has been designed. The filter is intended to be used as a channel-select filter for a zero-IF Bluetooth receiver. The frequency tuning scheme is simpler and has more relaxed specifications than conventional ones. The filter bandwidth is 0.5 MHz and the overall scheme dissipates 1.1 mA from a 1.8-V supply. The third-order intermodulation (IM3) distortion of the filter for a 1Vpp two-tone signal centered at 350 kHz is −67dB.

A CMOS highly linear voltage-controlled transconductor suitable for Gm-C filter design is presented. The control loop to program the transconductance maintains the input transistors in triode region with a compact topology. Measurement results for the transconductor fabricated in a 0.5-lm CMOS technology feature a spuriousfree dynamic range (SFDR) of 72 dB for 1 V pp differential inputs at 1 MHz. The voltage to current converter ensures a high linearity level for a wide transconductance range. Functionality of the transconductor is shown in a fifth-order Gm-C tunable complex filter well suited for a dual-mode Bluetooth/Zigbee transceiver.

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