# Carrier Triple Beat Test

Triple beat test is employed to mimic the cross-modulation distortion scenario and validate the performance in 3G and 4G/LTE devices. In Triple Beat test two tones and at Tx frequency and another tone at Rx frequency produces, intermod components at . If the two Tx tones are very close, then intermod components falls in Rx band. The highest power intermod component produced by triple beat test is 6dB higher than 3rd order intermod component produced by two tone test. This test is also called Carrier triple beat test (not composite triple beat test).

Consider a nonlinear amplifier whose input-output characteristic is represented by a 3rd order polynomial given by

(1)

where, is the output voltage of the amplifier
and is the input voltage applied to the amplifier

Consider three carrier frequencies, f1, f2 and f3. Any combination involving one sum and one difference will produce a triple beat component near the original third carrier frequency. If the carriers are close to each other, the inter-modulation product at frequencies () and () fall near the original carrier frequency .

(2)

where,
,
and
.

Substituting Eq.(2) in Eq.(1), and grouping the same order terms we get

(3)

Figure 1 shows the triple beat component produced due to beating two tones (f1 and f2) along with f3, and falling in the vicinity of thrid carrier tone(f3).

Figure 1. Triple beat test – RF carriers/tones and intermod components

Here carrier triple beat ratio is defined as ratio of fundamental component power to triple beat 3rd order intermod component power.

From Eq.(3),

(4)

At small signal levels, . So

(5)

In terms of power

(6)

where, IIP3 is 3rd order intercept point from two tone test

The highest power intermod component produced by triple beat test is 6dB higher than 3rd order intermod component produced by two tone test.

For further reading on the test setup, refer to the articles or application notes here [1], [2] and [3]

### References

[1] “K&L Microwave 3G, LTE/4G filter solutions for Intermodulation and Triple Beat testing.” [Online; Accessed Aug 2014]. Available: http://www.klmicrowave.com/catalog/KLMicrowaveIMDWebinar.wmv
[2] “Triple Beat and IMD for RF Switches, National Instruments .” [Online; Accessed Aug 2014]. Available: http://www.ni.com/white-paper/14506/en/
[3] “SKY13473–569LF: 0.4 to 2.7 GHz SP10T LTE Transmit/Receive Switch with MIPI RFFE Interface.” [Online; Accessed March 2015]. Available: http://www.skyworksinc.com/uploads/documents/SKY13473_569LF_202148F.pdf

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