Development of a temperature insensitive current controlled current source for LNA bias circuit applications

The research described in this thesis is concerned with the analysis, design and development of a novel temperature insensitive Current Controlled Current Source (CCCS), in bipolar technology, in order to provide accurate amplification of a Proportional To Absolute Temperature (PTAT) reference current. The output current of the CCCS is intended for application as the bias current for a bipolar Low Noise Amplifier (LNA) in order to minimise gain variations with temperature across the industrial temperature range (-40·C to 8S·C). The thesis begins with an explanation of key parameters concerned with LNA design and a target specification is defined. In Chapter 2, a conventional LNA, with constant with temperature bias current, is developed following a methodical approach based on conventional techniques. This meets the previously defined specification at room temperature but exhibits large gain variations with changes in temperature. The analysis and simulation results of this conventional LNA serve as a benchmark for comparison with later designs. In order to minimise any gain variations with temperature of a bipolar amplifier it is well known that the applied bias current should be PT AT. Thus, a thorough analysis and comparative review of traditional and novel PTAT reference current generator circuits is conducted in Chapters 3 and 4. Based on these findings the PTAT generator exhibiting best performance in terms of output current accuracy and insensitivity to power supply variations is presented. However, this circuit cannot accurately produce large rnA level currents necessary for LNA bias applications so that sufficient linearity of the LNA is maintained. Thus, a need for some form of accurate CCCS or Voltage Controlled Current Source (VCCS), which should be temperature insensitive in order to preserve the desired temperature coefficient of the reference current/voltage, is highlighted. Traditional VCCS/CCCS designs are investigated in Chapter 5. Limitations of these approaches leads to the design and development ofa novel CCCS with built in PTAT reference. The presented CCCS utilises a new, previously unseen, architecture and has led to a patent application [1]. The author has reported the majority of this work in technical literature [2-4]. In Chapter 6, the output of the novel CCCS is adapted to include the conventional LNA circuit designed previously in Chapter 2. The results of the combined LNA and CCCS are compared with the conventional LNA. The combined LNA and CCCS offers a dramatic reduction in gain variation with temperature