R2000 datasheet(19/75 Pages) ETC

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Indy® R2000 Electrical, Mechanical, & Thermal Specification

Figure 4-4: Theoretical Output After Self-jammer Cancellation Relative to Full Scale.

Minimizing the I and Q scaling factors optimizes the DC of the received signal. The normal receiver data path will be

used and the control block taps the DC information after the digital channel filter. In order to maintain the DC

information through the data path, the external AC-coupling capacitors must be temporarily bypassed. When the AC-

coupling is bypassed, a 50 kΩ resistor is added at the intermediate frequency low noise amplifier (IF-LNA) input to

improve the differential and common mode voltage handling of the IF-LNA. The external LC mixer is also

disconnected in SJC calibration mode. The Indy R2000 state machine handles the disconnection of the AC coupling

and the mixer load and the connection of the resistor at the IF-LNA input for SJC.

One complication of controlling the cancellation is that the relative orientation of the coordinate systems is not

accurately known. If, for instance, the scaling of the +I signal is changed, this could result in a DC change in both the

receiver I and Q signals. Another complication that must be handled by the calibration algorithm is that for strong

self-jammer levels, the receiver will compress unless the cancellation provides at least 10 dB of self-jammer

suppression. The calibration procedure can be split into three different modes (see also Figure 4-5):



Hold mode: current I and Q scaling values are held.



Full scan mode: a coarse grid of settings are evaluated.



Matrix scan mode: evaluate all 3x3 settings centered on the current setting.

The actual implementation is coded in a generic fashion so that the full scan mode and the matrix scan mode simply

are two configurations of one general mode.

Because the DC signal caused by the self-jammer corresponds to a strong signal even after successful cancellation,

it is important that the receiver data path gain is set low. Therefore all the receiver gain settings have been collected

into two registers. During normal receiver operation, the gain settings are taken from ANA_RX_GAIN_NORM

(register

0x450).

During

self-jammer

cancellation

scan,

the

gain

instead

temporarily

defined

ANA_RX_GAIN_SJC (register 0x451),

if the “reduce gain” bit is set (register 0x152).

The optimum SJC setting is found by minimizing the magnitude of the complex signal after the digital filter selection

multiplexer. In this way, the signal can either be filtered with the FIR or IIR channel filter, or not filtered at all by the

channel filter. This approach means that the time delay from when a setting is changed until the result can be

observed varies. To handle this variation, the settling time is programmable. The settling time is defined as the time

the controller waits after a change of the settings until the magnitude measurement is started. The measurement

time is also programmable to support tradeoff of measurement speed against accuracy. Both the settling time and

measurement time are set by register 0x150.

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