ADRF6518ACPZ-R7 datasheet(30/39 Pages) AD

30 / 39 page

ADRF6518

Data Sheet

Rev. A | Page 30 of 39

Figure 80. EVM vs. Input Power over Digital Modulation Type; Filter Bypass

Mode, Gain Code = 0000000, 1.5 V p-p Differential Output Level Maintained

Figure 81 shows the same four modulation types as in Figure 80,

but with the filter enabled. EVM is generally degraded due to

filter noise, as described in the Noise Characteristics section.

Figure 81. EVM vs. Input Power over Digital Modulation Type;

Filter Corner = 63 MHz, Gain Code = 0000000, 1.5 V p-p Differential Output

Level Maintained

Figure 82 shows a sweep over several output setpoints, from

1.5 V p-p to 5.0 V p-p. EVM only changes by a couple of

decibels for the full output range tested, which gives the user

flexibility in determining the level at which the output signal is

maintained. Although not shown in Figure 82, signals slightly

bigger than 5 V p-p have drastically degraded EVM, and loss of

lock can occur easily.

Figure 82. EVM vs. Input Power over Output Level; Filter Corner = 63 MHz,

QPSK, 50 MSPS, Gain Code = 0000000

Figure 83 shows the EVM for several different digital gain settings.

There is an approximate 2 dB to 3 dB of EVM degradation at

the following gain settings: VGA1 = 9 dB, VGA2 = 12 dB,

VGA3 = 12 dB, and postamplifier = 3 dB. This is due to the

noise figure of the ADRF6518 increasing with the lower gain

setting of VGA1 (VGA1 sets the noise figure for the part). This

correlation is shown in Figure 23, which shows about a 2 dB

increase in noise figure when the VGA1 digital gain is changed

from 15 dB to 9 dB.

Figure 83. EVM vs. Input Power over Gain Code; Filter Mode = 63 MHz, QPSK,

50 MSPS, 1.5 V p-p Differential Output Level Maintained

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QPSK

16QAM

256QAM

1024QAM

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QPSK

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1.5V p-p

2.0V p-p

2.5V p-p

3.0V p-p

3.5V p-p

4.0V p-p

4.5V p-p

5.0V p-p

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GAINS: 15dB/21dB/21dB/3dB

GAINS: 15dB/21dB/21dB/9dB

GAINS: 9dB/12dB/12dB/3dB

GAINS: 12dB/12dB/12dB/3dB

GAINS: 15dB/12dB/12dB/3dB

GAINS: 15dB/15dB/15dB/3dB

GAINS: 15dB/18dB/18dB/3dB

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