Design & analysis of forward DC-DC converter sequential switching circuit for x-band transmitter in a remote sensing satellite

Abstract

X-band satellite data transmitter in a remote sensing Satellite generates carrier of 8275 MHz and carry out QPSK Modulation with the Base-Band data. It Accepts the base-band data at 128 Mbps from the Base-band Data Handling system and processes the data using a gain block, 2Watt pre-amplifier and a 10W Solid state power amplifier. All these blocks are in main and redundant configuration, including the Power converter. QPSK Modulates the above data on X-band carrier and transmits it to ground after suitable amplification and filtering. These blocks uses GaAsFET in depletion mode configuration for amplification of the signal. The Gain block uses +5V, the preamplifier uses +6.5V and the power amplifier uses +9V as drain supply. When applying a DC bias, to a device in a common source configuration, negative gate voltage must be applied first, followed by a positive drain voltage. Conversely while removing DC bias, the drain voltage must be removed first, followed by the gate voltage. A GaAsFET, with drain voltage applied and zero or floating gate voltage, is likely to oscillate and may damage the device due to transient burn-out. Hence, in the case of a bias application, a new self sequencing DC-DC converter is recommended.