National Semiconductor LMH6515 Variable Gain Amplifier Datasheet

The LMH6515 is a high performance, digitally controlled variable gain amplifier (DVGA) that combines precision gain control with a low noise, ultra-linear, differential amplifier. It is typically used to drive a high performance ADC in a wide range of mixed signal and digital communication applications, such as mobile radio and cellular base stations, where automatic gain control (AGC) is required to increase system dynamic range. When used in conjunction with a high speed ADC, the system dynamic range can be extended by up to 32 dB. The LMH6515 has a differential input and output, allowing for large signal swings on a single 5V supply. It is designed to accept signals from RF elements and maintain a terminated impedance environment. The input impedance is 200Ω resistive. The output impedance can be selected as either 200Ω or 400Ω. A unique internal architecture allows for use with both single ended and differential input signals. The input signals to the LMH6515 are scaled by a highly linear, digitally controlled attenuator with 31 accurate 1 dB steps. The attenuator output provides the input signal for a high gain, ultra-linear differential transconductor. The transconductor's differential output current can be converted into a voltage by using the on-chip 200Ω or 400Ω loads. The transconductance gain is 0.1 Amp/Volt, resulting in a maximum voltage gain of +26 dB when driving a 200Ω load.

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