Сircuit Note CN-0320
December 2013
This circuit is a flexible, frequency agile, direct conversion IF-tobaseband receiver. A fixed conversion gain of 5 dB reduces the cascaded noise figure. Variable baseband gain is used to adjust the signal level. The baseband ADC driver also includes a programmable low-pass filter that eliminates out-of-channel blockers and noise.
The bandwidth of this filter can be dynamically adjusted as the bandwidth of the input signal changes. This ensures that the available dynamic range of the ADC that this circuit drive s is fully used .
The core of the circuit is an integrated IQ d emodulator with fractional - N PLL and VCO . With just one (variable) referenc e frequency, the PLL/VCO can provide and a local oscillator ( LO ) between 750 MHz and 1150 MHz. Precise quadrature balance and low output dc offsets ensure that there is minimal degradation of the error vector magnitude ( EVM ) .
The interface s between all of the components in this circuit are fully differential . Where dc coupling is required between stages, the bias levels of the adjacent stages are compatible with each other.
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Related datasheets:
Direct Conversion receiver Simplified Schematic (All Connections and Decoupling Not Shown)
