circuit is designed so that diode cr5 starts to conduct current near the saturation duty cycle of the circuit which includes diodes cr1 cr2 and cr6 this provides a transfer of function from a low current pulse to current converter which has relatively high voltage output to a converter which has lower voltage sensitivity and an operating range up to 100 duty cycle the output filtering of this circuit is capacitor c2 and resistor r6 and may be of a shorter time constant since this part of the circuit responds to higher pulse rates than capacitor c1 and resistor r3 for optimum human interface the two current outputs from resistors r3 and r6 are summed together and interact in resistor r7 by superposition resistor r7 represents the input impedance of a driven circuit not shown the signal on resistor r7 may drive a log amplifier whose output will display bit error rate over 6 decades of dynamic range while the example above is based on input pulses having a 1 u03bcsec pulse width this is clearly a designer 39 s choice other pulse widths may be used as long as the output circuit or some other portion of the system is calibrated.