Optimised RF input section for coplanar transmission line
A chip comprising a bonding pad region and a transmission section. The bonding pad region has a first impedance, and is configured for electrical connection to an external transmission line. The transmission section extends away from the bonding pad region and has a second impedance. The bonding pad region is configured to enable field confinement and field matching between the bonding pad region and the external transmission line, and the second impedance is not equal to the first impedance.
1. A system comprising:
an external transmission line, and
a chip comprising:
a bonding pad region comprising a signal pad and a ground pad, the bonding pad region having a first impedance and being connected to the external transmission line;
a transmission section extending away from the bonding pad region and comprising a signal electrode electrically connected to the signal pad and a ground electrode electrically connected to the ground pad, the transmission section having a second impedance;
wherein:
the transmission section comprises a first non-conductive gap between the signal electrode and the ground electrode, and the bonding pad region comprises a second non-conductive gap between the signal pad and the ground pad;
a width of the second non-conductive gap is less than a width of either the signal pad or the ground pad;
an impedance of the external transmission line is equal to the second impedance; and
the second impedance is not equal to the first impedance as a result of the width of the second non-conductive gap being less than the width of either the signal pad or the ground pad.
2. The system according to claim 1 , wherein the width of the second non-conducting gap is equal to a width of the first non-conducting gap.
3. The system according to claim 1 , wherein the width of the second non-conducting gap is less than 50% of the width of the signal or ground pad.
4. The system according to claim 1 , wherein the width of the second non-conducting gap is 80 microns or less.
5. The system according to claim 1 , wherein the transmission section comprises two ground electrodes spaced equidistantly each side of the signal electrode, and the bonding pad region comprises two ground pads spaced equidistantly either side of the signal pad, each electrically connected to a corresponding ground electrode.
6. The system according to claim 1 , wherein the transmission section is configured to process radiofrequency (RF) signals.
7. The system according to claim 1 , wherein the first impedance is less than the second impedance.
8. The system according to claim 1 , wherein the bonding pad region is about 100 microns or less in length.
9. The system according to claim 1 , wherein the chip is a LiNbQ 3 chip.
10. A modulator comprising the system according to claim 1 .