Patent ID: 6593774
Filing Date: 2003-07-15
Classification: H03K

Abstract:
An improved Emitter Coupled Logic (ECL) circuit based upon an ECL circuit of a conventional design wherein, while preserving the inherent advantages of a traditional ECL such as, but not limited to, high frequency operation, low propagation delay, ability to drive high cable load, low internal switching noise and high noise immunity to external noises, the improvement of the ECL circuit comprising one or more of the following embodiments with their respective additional advantages:addition of a capacitor coupling circuit, further comprising a network of a serial pass capacitor C and two bias resistors Rb1 and Rb2 powered with a supply voltage, connected to an input section of the ECL circuit of a conventional design such that a required quiescent current at the input section of the said conventional ECL circuit is provided by the powered bias resistors Rb1 and Rb2 and the RC-time constant of the said capacitor coupling circuit is made significantly longer than the clock period corresponding to a pre-determined minimum frequency of operation whereby the input terminals of the improved ECL circuit are made directly drivable by a CMOS transmitter while the said improved ECL circuit being capable of a range of high frequency operation up to 240 MHz with said pre-determined minimum frequency of operation corresponding to a maximum allowable pulse width of 500 &mgr;S; proper modification of the value of an emitter resistor that is part of an emitter resistance network of the said ECL circuit of a conventional design whereby a desired peak-to-peak amplitude of output voltage of 400 mV, different from an approximate value of 800 mV from the conventional design, is obtained; addition of a voltage shifting circuit, further comprising a selected number of serially connected, forward biased diodes and a resistor Rc branched to GND, connected to an output section of the ECL circuit of a conventional design such that the difference in threshold voltage between the conventional ECL circuit and an external CMOS receiver is essentially compensated for by the summation of the voltage drops across the said serially connected, forward biased diodes whereby the output terminals of the improved ECL circuit are made capable of directly driving an external CMOS receiver; addition of an alternative voltage shifting circuit, further comprising a selected number of cascaded transistors individually biased to their On-state and with their respective emitter resistors branched to GND, connected to an output section of the ECL circuit of a conventional design such that the difference in threshold voltage between the conventional ECL circuit and an external CMOS receiver is essentially compensated by the summation of the voltage drops across the base-emitter junction of the said cascaded transistors whereby the output terminals of the improved ECL circuit are made capable of directly driving, with a high current driving capability, an external CMOS receiver; and addition of a collector electrode switch network, further comprising a selected number of switching transistors, having their respective bases further tied to a number of external control signals, connected in series with the power supply terminals of the said ECL circuit of a conventional design whereby the output terminals of the improved ECL circuit, in addition to being switchable between their two normal logic states, are made controllably switchable into a third state of high impedance for bi-directional differential data transmission under a half duplexing mode whereby the said improved ECL circuit can be used to completely implement the bi-directional data transmission, with a specific interface of USB 2.0, between a computer and an electronic device.