volume55-number1 - Flipbook - Page 12
Table 2. Example RF Front-End Black Box Parameters
for the Two Modes
Wideband Digital Receiver Design Results and
Optimization
High Sense
10
15
31
17
5
The following performance heat maps are sensitivity analyses showing
instantaneous spur free dynamic range (DR, dB) for varying:
Bypass
–14
14
75
40
25
X
Processing bandwidth and RF input level
X
RF front-end IIP2 and RF input level
X
RF front-end NF and RF input level
Mode
G (dB)
NF (dB)
IIP2 (dBm)
IIP3 (dBm)
IP1dB (dBm)
Table 3 compares the front end and ADC black box parameters, and the resulting
overall cascade performance.
In the high sense mode, the limiting factor to dynamic range is the noise floor,
and so cascaded NF is prioritized. The front-end noise figure depends mostly
on the insertion loss of the front-end filtering required for interferer mitigation
(this example budgets 6 dB loss). This preselect filtering needs to sit before the
amplifier to be effective, as the amplifier will create multisignal IMD products.
Each scenario is run for the high sensitivity and bypass paths. The boxes
annotate favorable operating zones. The tables tell you the dynamic range
(SFDR), or distance down to the noise floor or highest IMD spur, for a given max
input signal level at Pin. For any given table, the static variables are set per the
previous chain parameters.
In bypass mode, we benefit from the extremely high linearity of the SOI technology. No tricks here as the amplifier limited linearity is simply switched out in
favor of higher linearity, lower gain, and higher NF.
As discussed in prior sections, the Bv selected in Figure 11 is dependent upon
waveform detection objectives. Lower Bv decreases the noise floor, improving
dynamic range at low Pin, but at the expense of slower FFT times. Inversely, high
Bv values increase the noise floor, and poor sensitivity limits dynamic range.
The likely operating zone is at a balance point in between.
Table 3. Example High Sense (top) and Bypass (bottom) Cascaded Performance; the Overall Column Is the
Cascaded RF Front End plus ADC All-In Performance
RF Front End
ADC
Overall
Units
DR (dB)
Pin (dBm)
61 –80
Bv (Hz)
–70
–60
–50
–40
–35
–30
–25
–20
–15
–10
1.00E+02
58
68
78
71
61
56
51
46
41
36
31
1.00E+03
48
58
68
71
61
56
51
46
41
36
31
Full Scale
–6.5
dBm
1.00E+04
38
48
58
68
61
56
51
46
41
36
31
NSD
–148
dBFS/Hz
1.00E+05
28
38
48
58
61
56
51
46
41
36
31
–154.5
dBFS/Hz
1.00E+06
18
28
38
48
58
56
51
46
41
36
31
1.00E+07
8
18
28
38
48
53
51
46
41
36
31
dB
1.00E+08
–2
8
18
28
38
43
48
46
41
36
31
Gain
10
0
NF
15
19.5
16.1
dB
IIP2
31
35
21.5
dBm
IIP3
17
20
9.2
dBm
Pi
–40
–30
PN
dBm
–91.2
RF Front End
ADC
Overall
dBm
Units
Full Scale
–6.5
dBm
NSD
–148
dBFS/Hz
–154.5
dBFS/Hz
–14
0
dB
NF
14
19.5
33.5
dB
IIP2
75
35
48.6
dBm
33.0
Gain
IIP3
40
20
Pi
–15
–29
PN
12
dBm
dBm
–97.8
dBm
Pin (dBm)
DR (dB)
64 –80
Bv (Hz)
–70
–60
–50
–40
–35
–30
–25
–20
–15
–10
1.00E+02
41
51
61
71
81
84
79
74
69
64
59
1.00E+03
31
41
51
61
71
76
79
74
69
64
59
1.00E+04
21
31
41
51
61
66
71
74
69
64
59
1.00E+05
11
21
31
41
51
56
61
66
69
64
59
1.00E+06
1
11
21
31
41
46
51
56
61
64
59
1.00E+07
–10
1
11
21
31
36
41
46
51
56
59
–10
1
11
21
26
31
36
41
46
51
1.00E+08 –20
Figure 11. Instantaneous spur free dynamic range (DR) vs. RF input level (Pin) and processing
bandwidth (Bv); high sensitivity (top) and bypass mode (bottom).
Figure 12 illustrates that, at low Pin levels, IIP2 is irrelevant as the sensitivity sets
the dynamic range. The mid-range performance is most sensitive to IIP2. Midrange input power levels might comprise most use cases, and as Pin increases
toward the high sense to bypass switch point, amplifier linearity, especially IP2,
is critically important. The superior IP2 of ADL8104 stands out over this important mid-range, preserving high dynamic range performance.
The bypass mode higher IIP2 allows the operating zone box to shift down to
follow the best dynamic range.
Analog Dialogue Volume 55, Number 1
