Transmit mixer with current mode input

摘要

A differential mixer (DM) used in a telecommunication radio transmitter operating with a 3 Volt supply and including a silicon bipolar cross-connected pair of differential amplifiers (A; B) for receiving a first input voltage (LO) at a high frequency, a pair of current sources (I1; I2), and a voltage-to-current MOS converter (VIC) for receiving a second input voltage (VIN) at a lower frequency. The converter is adapted to convert the low frequency voltage to a differential current (INN) and is coupled to the junction points of the amplifiers and the current sources. The converter further includes a regulated differential cascode circuit (P1; P2) to which the low frequency input voltage (VIN) is applied via resistors (RI1; RI2) and which is coupled to the supply terminals (VCC; GND) of the mixer via two pairs of constant current sources (PB1, PB2; NB1, NB2) respectively. Preferably, a constant reference voltage terminal (VCC/2) is applied to the gate electrode of the transistors (P1; P2) of the cascode circuit via an operational amplifier (O1; O2).