Current-mode CMOS logarithmic function circuit

摘要

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.

主权项

1. A current-mode CMOS logarithmic function circuit, comprising:
an operational transconductance amplifier (OTA) having an inverting voltage input, a non-inverting voltage input, and a current output Iout; a pair of CMOS transistors configured in a bias circuit connected to said OTA for providing a bias current ID for controlling amplitude of the current at the current output Iout; a first MOSFET adapted for receiving a reference current IX, the first MOSFET being configured in weak inversion mode and producing a voltage output connected to the non-inverting input of the OTA; and a second MOSFET adapted for receiving a current input Iin, the second MOSFET being configured in weak inversion mode and producing a voltage output connected to the inverting input of the OTA, wherein the OTA produces an amplified current at the current output Iout asIout=ID⁢ln⁡(IinIX)  when the reference current IX has a constant value.