Using VCO-OTA TIAs to Break the Gain, Linearity and Power Consumption Trade-offs in Passive Mixer based Direct-Conversion Receivers

Abstract

This paper demonstrates the use of very high DC gain of a VCO based OTA to break the trade-off between the conversion gain (CG) and the power consumption in a passive mixer direct-conversion receiver for a given noise and linearity performance. A process for selecting the parameters of a VCO-OTA based TIA is highlighted with an example where the receiver delivers 20MHz of RF bandwidth at various CG settings. Simulation results demonstrate up to 38dB and 18dB improvement in CG and operational dynamic range compared to an inverter based OTA and a two-stage OTA respectively for a given linearity, NF and power consumption. Up to 17.5dB and 7.7dB improvement in the LNTA P1dB is demonstrated for a given CG, NF and power consumption. Up to two orders of magnitude reduction in the effect of TIA output 3rd order non-linearity on the overall linearity performance of the receiver is demonstrated with a VCO-OTA TIA.