Remarkable growth in the demand for communications products and services, and especially in the requirements for portable communications devices, has driven consumer requirements for low-cost, small-form-factor, low-power RF (radio frequency) transceivers. In addition, the development of state-of-the-art wireless applications has encouraged consumers to expect both the convenience of extended connectivity and the benefit of enhanced services. RF transceivers that operate in compliance with multiple prevailing standards are instrumental, if not required, in the satisfaction of these objectives. In this regard, the capabilities of CMOS (complementary metal/oxide/semiconductor) and BiCMOS (bipolar/CMOS) VLSI (very large scale integration) technology are particularly well suited to the accommodation of very aggressive levels of mixed-signal integration, as well as to the provision of increasing functionality in a single-chip RF integrated circuit (IC) device.
However, the increasing density to which integrated RF circuit blocks are packaged in the same, or neighboring, integrated circuit devices has been attended by a number of operational challenges. Prominent among them is an aggravated susceptibility to electromagnetic interference (EMI) that may be propagated between circuits and devices. For example, with respect to densely packaged integrated circuit devices, and with respect to RF integrated circuits in particular, a current circulating in one loop in a device, or on a circuit board, may induce an interfering voltage at the input of another circuit or device. The likelihood of interference is exacerbated when the circulating current is an RF current that propagates to a circuit that is required to accept signals at the frequency of the EMI.
Conventionally, an interfering voltage may be reduced by one or more of the following methods: minimizing the loop area of either the transmitting or the receiving loop, increasing the distance between the transmitting and receiving loops, or shielding either or both the transmitting or the receiving loop. In the situation where an integrated circuit may be part of the receiving loop, it may be impracticable either to further minimize loop area or to provide shielding as a mechanism to reduce the induced interference. That is, the input loop of an integrated circuit consists essentially of a lead frame, having substantially fixed dimensions, and bond wires connecting the lead frame to the integrated circuit die. The dimensions and overall area of this part of the input loop are tightly controlled and fixed, but may not be reduced to zero. Furthermore, standard IC packaging does not provide even minimally effective shielding for this part of the input loop.
Accordingly, what is desired is a technique to improve the immunity of a receiving (IC) device from interfering signals that may arise in the proximity of the device.