HMC939A

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Attenuators are resistive circuit elements, electrical devices used to reduce the magnitude of an electric signal. Attenuators are usually found in remote radio systems in order to reduce the strength of the signal, thus minimizing the interference with other signals in the transmission path. Despite their common use, attenuators are not a popular component in most electronic machinery because of their relatively simple structure. However, modern attenuators are used in a variety of applications in digital signal generations, active noise cancellation, and sound recording.

The HMC939A is a high performance 4-pin amplified attenuator based on CMOS technology from Hittite Microwave Corporation. It is fabricated using CMOS 0.13 μm TI technology for enhanced linearity and wide dynamic range. This digitally controllable attenuator allows for precise control in most complex manual or automated systems.

The primary application of the HMC939A is for study amplifiers, particularly those amplifiers used in electrocardiogram (ECG) recordings, as it is robust enough to handle the high gain and wide frequency range requirements that such recordings require. It can also be used in UHF, VHF, and L-Band radio systems, where it can be used to reduce the strength of the signal thus reducing interference with other signals in the transmission path. Additionally, the HMC939A can be used in many other applications, such as active noise cancellation, sound recording, and digital signal generation.

The HMC939A is a fully integrated CMOS device that accomplishes control and operation with a single pin. The applications of the HMC939A are varied, as it can be used for gain adjustments in communication systems, as a voltage-variable attenuator, or as a digitally controlled amplifier. It has two analog input signals where the gain or attenuation can be adjusted using the control pin. The output impedance is 50 ohms and the voltage gain of the device is -2v/v. The power consumption and heat dissipation of this device are 1.9 mW and 0.025 W/°C respectively.

The working principle of the HMC939A is similar to other attenuators. It utilizes the ‘voltage-controlled-resistor’ (VCR) concept, which consists of an array of transistors, each acting as a separate resistor. The transistors are connected in parallel to form an array of resistances. An external voltage is applied to the gate of each transistor to determine its resistance value. Thus, when the control voltage changes, the resistance of each transistor changes accordingly, and the overall resistance of the VCR is adjusted. This in turn adjusts the gain or attenuation of the circuit.

In conclusion, the HMC939A is a high performance 4-pin amplified attenuator based on CMOS technology. It has robust enough features to be used in ECG recording amplifiers and for digital signal generation, active noise cancellation, and sound recording. The device utilizes the ‘voltage-controlled-resistor’ (VCR) concept, which is an array of transistors controlling the resistance and thus the gain or attenuation of the circuit.

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