Analog Devices ADRV9005 Reference Manual page 154

Reference Manual ADRV9001
RECEIVER/OBSERVATION RECEIVER SIGNAL CHAIN
The fe_gain_cw[7:0] is an 8-bit control word defined in the receiver gain table. Based on the information from the signal detectors, the gain
control algorithm finds the index of this gain table so that the corresponding gain control word at this index is used to calculate the gain at the
front-end attenuator. For more details, see the Receiver Gain Control section.
Mixer
The passive down converting mixer follows the RF attenuator. It down converts the RF signal to IF or baseband. The passive mixer uses a
non-overlapping ¼ duty cycle local oscillator generated by the four phases 50% duty cycle LO. The duty cycle distortion (DCD) circuit controls
the non-overlapping time. the DCD is implemented by delaying the rising edge of the 50% duty cycle LO.
Low Pass Filter (LPF)
In the receiver data chain, the LPF sits between the mixer and the ADC as a receiver baseband filter and supports a baseband 3dB bandwidth
of about 6.7 MHz to 40 MHz. It also converts the baseband signal current to voltage. The capacitor arrays are implemented to program the
various cut-off frequencies based on the system requirements. In addition, along with other AFE components, it provides a static gain of about
20 dB, which is independent of the gain control functionality through the receiver data chain.
The LPF can be configured in the transimpedance amplifier (TIA) mode with the single pole or in bi-quad (BIQ) mode with two complex poles
in the transfer function, which are denoted as first order LPF and second order LPF, respectively. The second order mode LPF has additional
out of band attenuation compared to the first order mode. Figure 149 and Figure 150 show the first and second order LPF simulated frequency
response at different f1db configurations. The second order mode LPF consumes about twice the power than the first order mode, and also
the in-band noise is around 2.5 dB worse than the first order mode. This is the tradeoff for the out-of-band rejection capability and power
consumption/in-band noise. The users rely on their application to choose either the first or second LPF order mode.
Figure 149. First Order RX LPF Frequency Response at Different f1db Configuration
Figure 150. Second Order RX LPF Frequency Response at Different f1db Configuration
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