R2000 datasheet(21/75 Pages) ETC

21 / 75 page

Indy® R2000 Electrical, Mechanical, & Thermal Specification

can demodulate correctly. The DC level change occurs during transition from transmit to receive. Varying

the time constant of the high-pass filtering or sample and holding the DC offset is allowed, provided the air

interface protocol is not violated.



The AC coupling capacitor and the bias resistance must form a low-pass filter for the bias thermal noise,

provided the total integrated noise is a constant equal to KT/C. To reduce the input referred noise of the

baseband low noise amplifier, you can either set the corner frequency high to reduce the in-channel

spectral noise density, or set the corner frequency lower than the high-pass filtering in the baseband filter

chain.



A bandpass filter is implemented at this node for DRM operation. This filter provides immunity from adjacent

and co-channel interferers. The topology shown in Figure 6 provides a 2nd order bandpass filter via the LC

tank and internal elements; this filter can provide immunity from adjacent interferers up to 2dBm at the input

of the Rx port.

To increase the noise bandwidth corner, ensure the following requirements are met:



The input impedance into the baseband amplifier must be high.



The coupling capacitor can be small; however, the high-pass DC notch corner may be too high.

To lower the noise bandwidth, ensure the following requirements are met:



The input impedance into the baseband amplifier can be low.



The coupling capacitor must be large. The requirements are as follows:

 The AC coupling capacitor must be charged within the protocol allowed wake-up time.1

 The high-pass filter in the baseband filter chain must attenuate the noise under the receiver noise floor.

 The choice of AC coupling capacitor size must be made in conjunction with the low noise baseband

amplifier design.

Figure 4-6: Receiver Front-end External Output Interface, including DRM LC Load of Mixer

5.2

Antenna Configuration Scenarios

There are two different use scenarios for the Indy R2000 reader chip based on the antenna subsystem. The first one

involves a single antenna configuration as shown in Figure 4-7.

This diagram is simplified, and doesn’t show filters,

baluns, or matching. For more detail, see section 5.3. In this application, a directional coupler is used to isolate the

transmit and receive paths. The antenna reflection of CW transmit power in receive mode dominates the receiver

It is possible to improve the charging time for the AC coupling capacitor with the help of a low resistance switch

to short the capacitor during the charging up phase. This approach will lower the time constant to enable a fast

charge phase even with a big value AC coupling capacitor.

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