Datasheet

LM1971
www.ti.com SNAS104B –FEBRUARY 1995–REVISED APRIL 2013
Figure 20. Active Reference with Active Gain Buffering
LOGARITHMIC GAIN AMPLIFIER
The μPot is capable of being used in the feedback loop of an op amp to create a gain controlled amplifier as
shown in Figure 21. In this configuration the attenuation levels from Table 1 become gain levels with the largest
possible gain value being 62 dB. For most applications, 62 dB of gain will cause signal clipping to occur.
However, this can be controlled through programming. It is important to note that when in mute mode the input is
disconnected from the output, thus placing the amplifier in open-loop gain state. In this mode, the amplifier will
behave as a comparator. Care should be taken with the programming and design of this type of circuit. To
provide the best overall performance, a high input impedance, low input bias current op amp should be used.
Figure 21. Logarithmic Gain Amplifier Circuit
MUTE FUNCTION
A major feature of the LM1971 is its ability to mute the input signal to an attenuation level of 102 dB. This is
accomplished internally by physically disconnecting the output from the input while also grounding the output pin
through approximately 2 kΩ.
The mute function is obtained during power-up of the device or by sending any binary data of 0011 1111 and
above serially to the device. The device may be placed into mute at any time during operation, allowing the
designer to make the mute command accessible to the end-user.
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