Integrated Attenuators for Controlled Reduction of RF Signals
When it comes to precisely reducing the amplitudes of RF signals, an attenuator is indispensable. Although there are linearly adjustable attenuation networks available that utilize special PIN diodes. They necessitate intricate control circuitry.
Simplified RF Signal Attenuation with Integrated Technology
A practical alternative is employing an integrated attenuator that operates in distinct steps. The RF 2420, an integrated circuit crafted using gallium-arsenide (GaAs) technology, covers a frequency range from 1 MHz to 950 MHz. This makes it suitable for attenuating cable television signals. The attenuation levels can be adjusted from 0 to 44 dB in 2-dB increments. It’s important to factor in an insertion loss of 4 dB during usage.
Setting and Controlling Attenuation Levels
The fundamental attenuation level, set at 0 dB, serves as the benchmark for switchable attenuation networks offering 2, 4, 8, 10, and 20 dB of attenuation. These levels are regulated through a series of 5 TTL inputs. Control signals must maintain Low levels below 0.3 V and High levels of at least +2.5 V. The RF 2420 operates within a supply voltage range of +3 V to +6 V, with a typical current consumption of 4 mA. Activating the power-down mode reduces the current consumption to 0.8 mA by cutting power from the bussed VDD- pins.
Minimal External Components Required
The sample circuit diagram for the RF 2420 reveals that only decoupling capacitors are necessary as external components. The input and output coupling capacitors determine the lower operating frequency limit, and the table provides suitable capacitor values. While the input and output are tailored for 50-ohm operation, they can also be used with 75-ohm cables, albeit with a slight increase in reflections.
Package and Additional Information
The RF 2420 is packaged in a 16-pin SOP-16 SMD format. More detailed information about its specifications and usage can be found in its datasheet, available at www.rfmd.com.
Understanding the PIN Diode
The PIN diode is a unique semiconductor diode where a high resistivity intrinsic layer is sandwiched between the P and N-regions. This design results in a substantial electric field between the P and N-region, defining its distinctive characteristics.