This invention relates to an integrated transceiver circuit packaged component.
One known such component is shown in FIG. 1 of the accompanying drawings together with an external filter 1. The transceiver has two modes of operation, transmit and receive. In both modes a local oscillator signal is generated by an on-chip voltage controlled oscillator (VCO) 3.
In the receive mode signals enter the transmit/receive (T/R) common port 5 at the RF frequency. The signal level is boosted by the low noise amplifier (LNA) 7 with the addition of very little noise. The off-chip band pass filter 1 then rejects all of the noise power at the image frequency (local oscillator frequency (LO)-intermediate frequency (IF), for an RF signal at LO+IF). Without filter 1 the image noise power would be down-converted to the IF along with the signal (and noise) at the RF frequency. A mixer 9 multiplies the RF and VCO signals and generates an IF signal at a frequency RF-LO (assuming RF is greater than LO). The IF signal is then amplified by a differential amplifier 11 prior to its output at port 13.
In the transmit mode a differential input signal at the IF frequency is input at port 15 and amplified by differential amplifier 12. Mixer 9 multiplies the output of amplifier 12 with the VCO signal to generate two `sidebands` at LO-IF and LO+IF. Assuming the RF signal is at LO+IF, then this is the wanted sideband and the LO-IF signal is termed the unwanted sideband. Filter 1 is used to reject the unwanted sideband and any other spurious mixing products/harmonics. The wanted RF signal is then routed back on chip and through a power amplifier 17 prior to output at the T/R common port 5.
The transceiver circuit further comprises an amplifier 23 connected to the output of VCO 3 for providing a phase locked loop (PLL) drive at output port 25 of the package.
With reference to FIG. 2 of the accompanying drawings, microwave integrated circuits (MICs) have a number of ground points all connected to a common ground plane. In the case of monolithic MICs (MMICs) this is normally the back side of the chip. When packaged it is normal to provide a low inductance ground (such as a metal based package) for the common chip ground. The inductance between the chip ground (internal to the package) and the circuit ground (external to the package) is termed the common lead ground inductance.
A fraction of the output signal is fed directly back to the input. At low frequencies, where the reactance of L.sub.COMMON is small, this has minimal effect, but as the frequency of operation increases so the reactance of L.sub.COMMON and hence the level of feedback increases. The presence of L.sub.COMMON causes feedback between each and every pin of the package. Differential signals do not suffer from this problem, only single-ended signals.
The transceiver configuration of FIG. 1 suffers from problems relating to common lead grounding inductance when low cost packaging is used. Common lead inductance serves to act as series feedback between each and every pin of the transceiver package. Just 0.2 nH will act as -20 dB of feedback (considering 50 ohm source and load impedances) at 2.4 GHz (the USA's ISM band). This causes the following problems:
1. Potential for instability in both transmit and receive paths as a result of loop gains greater than unity between port 5 and port 19 (the port by means of which filter 1 is connected to amplifiers 7, 17). PA1 2. Degradation of filter performance as a result of lowisolation between port 19 and port 21 (the port by means of which filter 1 is connected to mixer 9). PA1 3. Appreciable levels of transmit power fed back to the PLL drive port 25 (can cause a radio to loose lock).
One possible solution to these problems is to provide each ground connection point on the chip with an individual package pin for connection to the external ground. With circuits containing high levels of functionality, as the transceiver of FIG. 1, this results in a requirement for a package with a prohibitively large number of pins. Both cost and size of the end component are increased.