UTC571M データシートの表示（PDF） - Unisonic Technologies

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UTC571M

LINEAR INTEGRATED CIRCUIT / COMPANDER

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UTC571

LINEAR INTEGRATED CIRCUIT

At very low input signal levels the bias current of Q 2 , (typically 50nA), will become significant as it must be

supplied by Q 5 . Another low level error can be caused by DC coupling into the rectifier. If an offset voltage exists

between the V IN input pin and the base of Q 2 , an error current of V OS /R 1 will be generated. A mere 1mV of

offset will cause an input current of 100nA which will produce twice the error of the input bias current. For highest

accuracy, the rectifier should be coupled into capacitively. At high input levels the β of the PNP Q 6 will begin to

suffer, and there will be an increasing error until the circuit saturates. Saturation can be avoided by limiting the

current into the rectifier input to 250mA. If necessary, an external resistor may be placed in series with R 1 to limit

the current to this value. Figure 7 shows the rectifier accuracy vs input level at a frequency of 1kHz.

+1

0

-1

-40 -20 0

RECTIFIER INPUT dBm

Figure 7. Rectifier Accuracy

At very high frequencies, the response of the rectifier will fall off. The roll-off will be more pronounced at lower

input levels due to the increasing amount of gain required to switch between Q 5 or Q 6 conducting. The rectifier

frequency response for input levels of 0dBm, -20dBm, and -40dBm is shown in Figure 8. The response at all three

levels is flat to well above the audio range.

INPUT=0dBm

0

-20dBm

3

-40dBm

10K

1MEG

FREQUENCY(Hz)

Figure 8. Simplified ∆G Cell Schematic

YOUW ANG ELECTRONICS CO.LTD

9

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