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By incorporating a unique architecture with 6-b digital control, these amplifiers blend wide dynamic ranges with precisely adjustable gain over wide frequency spans.
Signal amplification is a key function in high-frequency radios. Many newer wireless- communications systems rely on maintaining stable amplitude within the radio's downconversion circuitry even when faced with a wide range of input signal levels. Because of this, the variable gain amplifier (VGA) has become an essential building block in many wireless radio transceivers. Traditional VGAs have varied the DC voltage to set the amplifier's gain, although additional circuitry and printed-circuit-board (PCB) space were needed for driver circuitry capable of providing precise control voltages. Hittite Microwave (www.hittite.com) has developed an alternative: the digital VGA [DVGA] (Fig. 1). It features the performance of traditional analog VGAs, with the simplicity of a digital control interface and the added benefits of wide bandwidth, minimal need for additional components, and minimal use of PCB space.
The new DVGAs were born out of the market need to finely control the gain increments and maintain increased stability over a wider frequency range. Important design requirements included wide dynamic range, with high output third-order intercept point (OIP3) and low noise figure, but also a wide gain control range with fine-resolution steps, uniformity in performance across frequency and different gain levels, and monotonicity in gain tuning across a wide operating bandwidth. The resulting DVGAs, models HMC625LP5E, HMC626LP5E, and HMC627LP5E (see table), are designed to cover all of the major wireless standards/bands, including Global System for Mobile Communications (GSM), code-division-multiple-access (CDMA) cellular, wideband CDMA (WCDMA), Universal Mobile Telecommunications Service (UMTS), wireless local-area networks (WLANs), and WiMAX applications. All three variable-gain amplifiers are housed in a tiny 5 Δ 5-mm plastic QFN leadless surface-mount packages (LP5E leaded versions are also available for all models) so that users have the flexibility to interchange devices for specific system needs. All three DVGAs offer total gain-control range of 31.5 dB, achieved through combinations of signal attenuation and positive gain.
For example, model HMC625LP5...