Phase shifters and attenuators implementation for active transmitter signal cancellation in the receiving path for SDR

Many wideband duplex SDR applications do not use a receiver (RX) bandpass filter, so the low-noise amplifier (LNA) in the receive path must have a higher dynamic range, which comes with an increase in power consumption. To solve this problem, active transmitter signal cancellation in the receive path is used. These capabilities are considered for 5G New Radio Wireless Transceivers, for Multiple Input Multiple Output (MIMO) systems and radar applications. Solutions for the implementation of individual units, such as a delay line, digital applications, including in conjunction with analog, for various radio wave propagation channels and using neural networks are actively considered in modern literature. This paper considers options for implementing phase shifters and attenuators required for this device. The simulation of the considered implementation options for phase shifters and attenuators examples showed that the resistive digital step attenuator with a switch on MOSFETs and the attenuator on P-I-N diodes are not recommended for implementing the attenuator and phase shifter blocks of the compensation circuit. Active digital step MOS attenuator based on weighted current summation has a good dynamic range, but the output noise level seems too high over the entire possible current range. Therefore, this circuit needs noise optimization to be proposed for practical implementation. Active digital step MOS attenuator based on the composition of weighted current sources has intermodulation distortions less than –40 dB, a small parasitic phase shift and a low noise level. The high dynamic range allows installing a fixed attenuator and further reducing the output noise.