Design and implementation of an electrical interface for ring modulators using CPWs

This work presents the design and implementation of an electrical interface using coplanar waveguides (CPWs) to drive high speed ring modulators. To show this, first a small-signal model (SSM) of the modulator is developed by measuring its S11 response. The SSM is simulated with a conventional CPW to highlight the reflection problem emerging from the mismatch between the 50 Omega system reference and the high input impedance of the ring modulator which is around 1kOmega. The mismatch problem is mitigated by the proposed five-pin CPW design with ground-signalground- signal-ground (GSGSG) structure which terminates the reflection into an external 50 Omega termination. The proposed CPW demonstrates a measured S11 magnitude response below -15 dB throughout the frequency range of 25 GHz and -10 dB until 40 GHz.