Antenna Filter

Co-location Deployment Considerations for Direct RF Sampling Transceivers (WP541)
Document ID
WP541
Release Date
2022-01-11
Revision
1.0 English

The antenna filter must filter the 16 dBm blocker to a level such that:

  • It does not overdrive the LNA.
  • The HD2 and IM2 generated by the LNA is lower than –109 dBm, referenced to the antenna input.
The LNA and gain blocks tuned for the C-band are generally optimized at 3800 MHz and have reduced dynamic range performance at 1900 MHz in the form of P1dB, IP2, and IP3. The Qorvo QPL9058 (operating with 3.3 VDD) and QPA9127 specifications are summarized in the following table. The IP2 specification for the devices is not published in the datasheets. The values used are from actual measurement using the respective evaluation kit.
Note: At 1900 MHz, the gain is usually about the same as at 3800 MHz while the IP2/IP3 are significantly worse.
The QPL9058 LNA can be operated at two supply voltages, 5.0V and 3.3V. 3.3V VDD is used here for lower power at the expense of linearity. The data in the following table is quoted for 3.3 VDD unless otherwise noted.
Table 1. Specifications for RX Amplifiers at 1900 MHz and at 3800 MHz
QPL9058 (3.3 VDD) QPA9127 (5 VDD)
Parameter At 3800 MHz At 1900 MHz At 3800 MHz At 1900 MHz
Gain 17.4 dB 18 dB 21 dB 20 dB
Output P1dB 17.6 dBm 15 dBm 19.5 dBm 19.5 dBm
Output IP3 33 dBm 26 dBm 35 dBm 33 dBm
Output IP2 (2 tones)

40 dBm (3.3 VDD)

46 dBm(5 VDD)

29 dBm (3.3 VDD)

33.5 dBm (5 VDD)

 32.5 dBm
Input IP2 (referenced to antenna input)

22.6 dBm (3.3 VDD)

28 dBm (5 VDD)

11 dBm (3.3 VDD)

16 dBm (5 VDD)

 12.5 dBm
Noise figure 0.6 dB 0.4 dB 1.4 dB 1.2 dB
  • To meet goal #1 with 10 dB of margin, the antenna filter rejection at 1900 MHz needs to exceed 29 dB.

    16 dBm + 18 dB gain – filter rejection(dBm) ≤ 15 dBm – 10 dB margin

  • To meet goal #2 using the IP2 formula IMD2 = 2*Power_in – IIP2

    2*Power_in – 11 dBm ≤ –109 dBm → Power_in ≤ –49 dBm

Which means the antenna filter rejection at 1900 MHz needs to be at least 16 dBm – (–49 dBm) = 65 dB.

This is more stringent than goal #1 and similar to that of the TX emission filter requirement of 62 dB. This requirement is independent of the type of ADC architectures used and, as previously noted, filters with 75 dB of rejection are commonly available. Without loss of generality, an antenna filter rejection of 70 dB at 1900 MHz is assumed for the subsequent analysis.