Analog Devices AD8362 Product Info

• Complete fully calibrated measurement/control system
• Accurate rms-to-dc conversion from 50 Hz to 3.8 GHz
• Input dynamic range of >65 dB: −52 dBm to +8 dBm in 50 Ω
• Waveform and modulation independent, such as GSM/CDMA/TDMA
• Linear-in-decibels output, scaled 50 mV/dB
• Law conformance error of 0.5 dB
• All functions temperature and supply stable
• Operates from 4.5 V to 5.5 V at 24 mA
• Power-down capability to 1.3 mW

The AD8362 is a true rms-responding power detector that has a 65 dB measurement range. It is intended for use in a variety of high frequency communication systems and in instrumentation requiring an accurate response to signal power. It is easy to use, requiring only a single supply of 5 V and a few capacitors. It operates from arbitrarily low frequencies to over 3.8 GHz and accepts inputs from −52 dBm to +8 dBm with crest factors that are typical of quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM) modulation schemes.

The input signal is applied to a resistive ladder attenuator that comprises the input stage of a variable gain amplifier (VGA). The 12 tap points are smoothly interpolated using a proprietary technique to provide a continuously variable attenuator, which is controlled by a voltage applied to the VSET pin. The resulting signal is applied to a high performance broadband amplifier. Its output is measured by an accurate square-law detector cell. The fluctuating output is then filtered and compared with the output of an identical squarer, whose input is a fixed dc voltage applied to the VTGT pin, usually the accurate reference of 1.25 V pro-vided at the VREF pin.

The difference in the outputs of these squaring cells is integrated in a high gain error amplifier, generating a voltage at the VOUT pin with rail-to-rail capabilities. In a controller mode, this low noise output can be used to vary the gain of a host system’s RF amplifier, thus balancing the setpoint against the input power. Optionally, the voltage at VSET can be a replica of the RF signal’s amplitude modulation, in which case the overall effect is to remove the modulation component prior to detection and low-pass filtering. The corner frequency of the averaging filter can be lowered without limit by adding an external capacitor at the CLPF pin. The AD8362 can be used to determine