Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Logarithmic
Patent
1994-10-04
1996-02-06
Tran, Toan
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Logarithmic
327350, 327 65, 327 52, G06F 7556, G06G 720, H03K 522
Patent
active
054898684
ABSTRACT:
A detector cell for a logarithmic includes a differential pair of inputs across which a input signal V.sub.0 is applied across. The detector cell also includes a pair of differential outputs. The detector cell is comprised of three transistors Q4, Q5 and Q6. Resistors are coupled between the bases of adjacent transistors. The resistors form a voltage divided across which the input signal V.sub.0 is divided. The emitters of the three transistors are coupled to a current source, which sends a predetermined amount of current Ihd D. The collectors of the first and third transistors are coupled together to form a first differential input of the differential input pair. The collector of the second transistor alone forms the second differential input of the pair. The emitter area of the second transistor is ratioed with respect to the first and third so that a current I.sub.1 flowing through the first differential output is equal to a current I.sub.2 flowing through the second differential output when no input signal is applied across the differential inputs of the detector. A difference amplifier is coupled to the differential outputs to compare the currents I.sub.1 and I.sub.2 flowing therethrough. The difference amplifier produces an output current I.sub.OUT that is proportional to the difference between the two currents I.sub.1 and I.sub.2. Because currents I.sub.1 and I.sub.2 are equal when no input signal is detected, the difference amplifier produces an output current I.sub.OUT that is approximately zero. A load resistor is coupled to output of the difference amplifier to convert the current I.sub.OUT to the desired output voltage signal V.sub.RSSI.
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Gilbert, Barrie, "Current-mode Circuits From A Translinear Viewpoint: A Tutorial" from Analogue IC Design: The Current-mode Approach, Toumazou, Lidgey, Haigh, eds. Peter Peregrinus, Ltd., London 1990.
Analog Devices Inc.
Tran Toan
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