Application: Fast Four-Quadrant Current Multiplier

Abstract

In this chapter a fast four-quadrant current multiplier based on the MOS translinear (MTL) circuit principle is presented [1], [2]. The circuit is an example of how a desired transfer function can be realized by a combination of basic MTL functions, as described in chapter 4. Two current squaring circuits are used to implement the four-quadrant multiplication function using the well-known quarter-square principle. The current squaring circuits are implemented in an up-down loop topology, which results in a relatively large -3dB bandwidth. Simulations indicate that a bandwidth of 50 MHz is feasible using transistor channel lengths of 10µm. The influence of second-order effects on the behaviour of the multiplier is analyzed by applying the relations derived in chapter 2. The multiplier circuit illustrates that MTL circuits can yield a good performance in spite of the fact that the square-law behaviour of an MOS transistor is much more influenced by second-order effects than the exponential behaviour of bipolar transistors.