Patent ID: 8779833

Claim:
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 I out ; a pair of CMOS transistors configured in a bias circuit connected to said OTA for providing a bias current I D for controlling amplitude of the current at the current output I out ; a first MOSFET adapted for receiving a reference current I X , 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 I in , 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 I out as I out = I D ⁢ ln ⁡ ( I in I X ) when the reference current I X has a constant value.