The opto-electronic high-frequency transconductor and circuit applications

A new hybrid design approach for high gain high frequency opto-electronic transconductors is proposed. The idea exploits the high output resistance of a p-i-n photodiode to realise a high resistance current source. Measured results on a discrete circuit implementation of a bandpass filter using laser diodes, p-i-n receivers and discrete Si JFETs demonstrates that foQ products of more than an order of magnitude higher than device process f_T can be obtained. Simulated results of a similar filter employing CMOS technology for the front-end FET shows that using realistic device models filter Qs of the order of 800 can be achieved at 100 MHz. Finally a GaAs based cascode op-amp is realised using LEDs and PIN diodes to realise the opto-electronic current sources and simulations show that voltage gains of the order 80 dB with 5 GHz unity gain bandwidth products can be achieved