Single-ended to differential transducer circuit

Abstract

A BALUN circuit (20) for low voltage operation for receiving single ended input signal at an input terminal (24) and providing a differential output signal across a pair of output terminals (OUT+, OUT-) is disclosed. The BALUN circuit (20) comprises a first branch including an input terminal (24) for receiving a single ended input voltage signal(RFin), a transistor (Ql), a resistance (Rl) (28), aresistance (RL), and an output terminal(OUT+). A second branch includes a transistor (Q3), a resistance (RL) and an output terminal(OUT-). An operational amplifier (26)maintains current flowing through the resistances RL in the first and second branches substantially equal to each other, in dependence upon the output voltage signal across the output terminals (OUT+, OUT-).

Description

technical field [0001] The present invention relates to unbalanced / balanced converter (BALUN) circuits, and in particular, but not exclusively, to BALUN circuits for connecting low noise amplifiers of radio frequency (RF) equipment to mixers. Background technique [0002] The RF signal provided by the antenna and LNA is usually single-ended, but a balanced circuit is usually used in the RF path of the integrated receiver / transmitter. Balanced circuits increase the immunity of RF circuits to common-mode disturbances and are therefore highly valued in RF circuit design. [0003] While differential antennas can be used to provide a balanced RF input signal, for simplicity a passive BALUN is often used to convert the unbalanced antenna signal into a balanced signal. However, the use of passive BALUNs has certain disadvantages. The passive balun is a lossy element whose loss occurs before the low noise amplifier to which the antenna is connected. Since the insertion loss is eq...

AI Technical Summary

Problems solved by technology

[0007] However, the circuit of Figure 1 has the disadvantage that the circuit cannot operate at a minimum supply voltage of 1.6 volts, therefore, for linearity and matching purposes, a feedback resistor R2 is required

Furthermore, there is no means for changing the phase characteristics of the circuit to obtain broadband operation, moreover, there is no means for compensating the current offset after the two differential sections

Images