CN-0150 Datasheet, PDF (3/5 Pages) Analog Devices – Software-Calibrated, 1 MHz to 8 GHz, 60 dB RF Power Measurement System Using a Logarithmic Detector

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CN-0150
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Figure 4. Input = 900 MHz, ADC Using an External 2.5 V Reference
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Figure 7. Input = 2.2 GHz, ADC Using an Internal 2.5 V Reference
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Figure 5. Input = 1.9 GHz, ADC Using an Internal 2.5 V Reference
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Figure 6. Input = 1.9 GHz, ADC Using an External 2.5 V Reference
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Figure 8. Input = 2.2 GHz, ADC Using an External 2.5 V Reference
COMMON VARIATIONS
The AD7887 is a 2-channel, 12-bit ADC with an SPI interface.
The second input channel of this device can be connected to the
AD8318 TEMP pin. This provides a convenient measure of the
ambient temperature around the AD8318. Like the AD8318
power measurement output, the TEMP voltage output should
also be calibrated.
If the end application requires only a single channel, the 12-bit
AD7495 can be used. In multichannel applications that require
multiple ADCs and DAC channels, the AD7294 can be used.
In addition to providing four 12-bit DAC outputs, this subsystem
chip includes four uncommitted ADC channels, two high-side
current sense inputs, and three temperature sensors. Current
and temperature measurements are digitally converted and
available to read over the I²C-compatible interface.
The temperature stability of the circuit can be improved using an
external ADC reference. The AD7887 internal 2.5 V reference has
a 50 ppm/°C drift, which is approximately 15 mV over a 125°C
range. Because the detector has a slope of −24 mV/dB, the ADC
reference drift contributes approximately ±0.3 dB to the temperature
drift error budget. The AD8318 temperature drift is approximately
±0.5 dB over a similar temperature range. (This varies with
frequency. See the AD8318 data sheet for more details.)
Rev. C | Page 3 of 5