Stretching the band with LDMOS

Stretching the band with LDMoS

Currently, E&I uses DMOS Fets in our Power Amplifiers, but now we are developing a new line of amplifiers with higher bandwidth capabilities using LDMOS. (MOSFET just stands for Metal-Oxide-Semiconductor-Field Effect Transistor, the “D” stands for diffused and the “L” for Lateral)

So what? – you ask!

Well there are several advantages with LDMOS. Firstly, the Drain connection is made to the top of the chip and the Source to the bottom of the chip. This means that it can be mounted directly to the copper flange of the device package offering much better thermal resistance over the DMOS which has to have a BeO insulator between the die and the flange. Better thermal resistance means lower die junction temperatures and that means even higher reliability.

Secondly, due to the parasitic capacitances inherent in the DMOS configuration, the upper end of the band is limited. LDMOS can work into the GHz region. And due to the lower capacitances, it is easier to make a broadband circuit.

Our engineering team has just developed a circuit that operates from 1 to 500 MHz, a bandwidth of 9 octaves with a gain flatness of +/- 1 dB. The circuit produces 10 Watts operating in class A. The design employs an ST Microelectronics transistor, the SD56120. These circuits will be put in parallel to produce power levels up to 100 Watts and above.

This is the performance data for a new circuit design.