HMC714LP5 Datasheet, PDF (36/40 Pages) Hittite Microwave Corporation – DUAL RMS POWER DETECTOR 0.1 - 3.9 GHz

v05.0309
HMC714LP5 / 714LP5E
DUAL RMS POWER DETECTOR
0.1 - 3.9 GHz
PAR – Envelope Power Normalized To Average Power (Continued)
The INS_A (INS_B) output is highly independent from input signal frequency, input average power, and temperature.
Proprietary design techniques assure very little part-to-part variation and maintain a very high degree of match
between channels.
2. A measurement of peak-power normalized to average power
To measure peak power, a peak-hold mechanism is required at the INS_A (INS_B) output. The
peak-hold circuit can be as simple as an RC combination on the INS_A (INS_B) pin. In this
configuration, peak excursions of the input signal is stored as a peak voltage on the external
Cext capacitor. Rext is used to set the quiescent bias point of Q1, and together with Cext
will for a time-constant for the peak-hold function. The larger Cext is the longer the peak-
detector will “remember” the largest signal excursion; conversely a smaller value of Cext will
result in a shorter memory, and less filtering. The value of Rext for this “peak-power” mode
of the iPAR function should be much larger than the value used for the iPAR mode described
previously (instantaneous power tracking mode) to extend the RextCext time-constant.
INS_[A,_B] = IREF_[A,_B] + SF*(PAR_[A,_B] - 1)
where IREF_[A,_B] = VCC_[A,_B] / 3 + 0.15V ≈ 1.82V (for VCC = 5V, R_EXT = 500 kΩ)
where PAR_[A,_B] = input signal peak-to-average ratio on channel [A,B]
and SF = the scaling factor set by an external voltage applied to V_TGT (150 mV when V_TGT = 2.0V)
The graphs below describes the INS_A (INS_B) peak-hold levels as a function of input peak-to-average ratio (PAR) and
also crest factor. Note how the voltage applied at V_TGT affects the INS_A (INS_B) reading. The voltage applied to the
V_TGT pin also has a secondary effect on crest-factor performance. The V_TGT signal optimizes internal bias points for
measurement accuracy at higher crest factors: refer to the section under “Adjusting V_TGT for greater precision” for a
iPAR Feature Peak-to-Average Power
Detection Configuration (R_EXT = 500Ω,
C_EXT = 100 nF)
3.4
3.2
INSA
3
Linear Fit
2.8
2.6
VTGT=2V
2.4
2.2
2
VTGT=1V
1.8
1.6
1
Single Tone (CW) Inputs
2 3 4 5 6 7 8 9 10 11 12
PEAK TO AVERAGE POWER RATIO (PAR)
iPAR Feature Peak-to-Average Power
Detection Configuration vc Crest Factor
(CEXT = 100 nF)
3.4
3.2
VTGT=2V Rext=100kohm
3
VTGT=2V Rext=500kohm
VTGT=1V Rext=500kohm
2.8
2.6
256QAM (1Mbps)
Crest Factor~7.8dB
2.4
2.2 Single Tone
(CW) Inputs
2
1.8
1.6
2 3 4 5 6 7 8 9 10 11 12 13 14
INPUT CREST FACTOR (dB)
12
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20 Alpha Road, Chelmsford, MA 01824 Phone: [phone] Fax: [phone]
Order On-line at www.hittite.com
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