Abstract: A CMOS logarithmic current generator includes current mode circuitry having a design principle based on a Taylor's series expansion that approximates an exponential function. A MOSFET circuit provides a function generator core cell having a biasing current Ib. The FETs of the circuit are matched and are biased in the weak inversion region. Additional transistors are used to convert a pair of input currents to a pair of voltages to provide an output current based upon a current mode logarithmic function. The biasing current Ib can be varied to provide a variable gain in the circuit.

Abstract: The high dynamic range exponential current generator produces an output waveform (current/voltage) which is an exponential function of the input waveform (current/voltage). The exponential characteristics are obtained in BiCMOS or Bipolar technologies using the intrinsic characteristics (IC/VBE) of the bipolar transistors. The high dynamic range exponential current generator is biased in weak inversion region. MOSFETs biased in weak inversion region are used not to utilize the inherent exponential (IDS/VGS) relationship but to simply implement x2 and x4 terms using translinear loops. The term x4 is realized by two cascaded squaring units. The approximation equation used is ? x ? 0.025 + ( 1 + 0.125 ? x ) 4 0.025 + ( 1 - 0.125 ? x ) 4 .

Abstract: The high dynamic range exponential current generator produces an output waveform (current/voltage) which is an exponential function of the input waveform (current/voltage). The exponential characteristics are obtained in BiCMOS or Bipolar technologies using the intrinsic characteristics (IC/VBE) of the bipolar transistors. The high dynamic range exponential current generator is biased in weak inversion region. MOSFETs biased in weak inversion region are used not to utilize the inherent exponential (IDS/VGS) relationship but to simply implement x2 and x4 terms using translinear loops. The term x4 is realized by two cascaded squaring units. The approximation equation used is ? x ? 0.025 + ( 1 + 0.125 ? x ) 4 0.025 + ( 1 - 0.125 ? x ) 4 .

Abstract: A CMOS logarithmic current generator includes current mode circuitry having a design principle based on a Taylor's series expansion that approximates an exponential function. A MOSFET circuit provides a function generator core cell having a biasing current Ib. The FETs of the circuit are matched and are biased in the weak inversion region. Additional transistors are used to convert a pair of input currents to a pair of voltages to provide an output current based upon a current mode logarithmic function. The biasing current Ib can be varied to provide a variable gain in the circuit.

Abstract: The current-mode CMOS logarithmic function circuit provides an ultra-low power circuit that produces an output current proportional to the logarithm of the input current. An OTA (operational transconductance amplifier) constructed from CMOS transistors, in combination with two PMOS transistors configured in weak inversion mode for providing a reference voltage input and a voltage input from the input current to the OTA, provides the circuit with a high dynamic range, controllable amplitude, high accuracy, and insensitivity to temperature variation.

Abstract: The current-mode CMOS logarithmic function circuit provides an ultra-low power circuit that produces an output current proportional to the logarithm of the input current. An OTA (operational transconductance amplifier) constructed from CMOS transistors, in combination with two PMOS transistors configured in weak inversion mode for providing a reference voltage input and a voltage input from the input current to the OTA, provides the circuit with a high dynamic range, controllable amplitude, high accuracy, and insensitivity to temperature variation.