Wide dynamic input range transconductor-based amplifier circuit for speech signal processing

摘要

A two-opamp gain stage wide dynamic range automatic level control circuit (WDR ALC) for implementation in a speech applications is disclosed. The first gain stage is formed by an inverting opamp with a transconductor device in the feedback loop. The first gain stage produces an output voltage which is coupled to a second gain stage via an ac coupling capacitor. The second gain stage is formed by an inverting opamp which produces the output voltages for the (WDR ALC). A fraction of the first stage's output voltage is fed back to the transconductor device. The transconductor device acts as a voltage controlled resistor that is effectively parallel with the feedback resistor of the first stage opamp. The output voltage of the second stage is fed back to peak detector adapted for speech electronic circuitry applications. The output of the peak detector is compared with a preset peak voltage by a converter which generates the control voltage for the transconductor device. Upon being activated, the transconductor device sinks a fraction of input current that is proportional to the output voltage of the first stage which effectively reduces the gain of the first stage. The gain reduction of the first stage suppresses the output voltage of the second stage to control the over gain of the (WDR ALC). The object of having an automatic level control circuit (ALC) operational over a broad range of input voltages is accomplished by virtue of having the input voltage applied directly to the first gain stage which is not affected by the transconductor device. The relaxation of the dependency of performance of the ALC on a transconductor device results in simplifying the design of the transconductor device.