HMC714LP5 Datasheet, PDF (35/40 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
12
12 - 148
iPAR – Envelope Power Normalized To Average Power
The INSA and INSB are envelope detector outputs for A & B channels that provide a measurement of instantaneous
signal power normalized average power. This feature is called Instantaneous Peak to Average Ratio (iPAR). The iPAR
makes peak-to-average power comparisons immediately obvious. This simultaneous measurement of envelope power
and average power in HMC714LP5E has two fundamental advantages over traditional methods of which employ two
different power detectors working in parallel.
• Both the iPAR and RMS detectors share the same measurement structures, and
• Both the iPAR and RMS detectors share the same temperature compensation mechanisms.
With traditional implementation of peak-to-average power detection, the dominant source of errors is due to the
uncorrelated measurement deviations between the two separate detectors. Both detectors in the HMC714LP5E share
the same circuits (INS_A-RMS_A pair and INS_B-RMS_B pair), so any deviations, however small, are fully correlated.
The iPAR feature can be configured to provide two major functions:
1. A measurement of instantaneous signal power normalized to average power
In this most basic measurement mode, INS_A (INS_B) output is terminated to ground using an
external resistor which forms an output buffer with the internal transistor Q1 connected in
emitter-follower configuration. With Rext = 3.9 kOhm (R20 and R12 on the evaluation board
for A & B channels), INS_A (INS_B) output can track the input envelope up to a modulation
bandwidth of 35 MHz at which point the output swing drops by 50%. For an unmodulated input
signal with f>>35 MHz, the INS_A (INS_B) output will provide a constant value of approximately
1.6V indicating that the instantaneous power is equal to the average power.
The INS_A (INS_B) output voltages linearly follow the instantaneous power levels at the detector
input with the transfer gain scaled by an external voltage applied to V_TGT (pin 28). For a
nominal voltage of 2V on V_TGT the scaling factor of the INS_A (INS_B) output is 200 mV.
INS_[A,_B] = IREF_[A,_B] + SF*(EAR_[A,_B] - 1)
where IREF_[A,_B] = (VCC_[A,_B]*R_EXT) /( 3*(R_EXT+65 Ohm)) ≈ 1.6 V (for VCC = 5V, R_EXT = 2 kΩ)
where EAR_[A,_B] = input signal RF AM envelope-to-average power ratio on channel [A,B]
and SF = the scaling factor set by an external voltage applied to V_TGT (200 mV when V_TGT = 2.0V)
For example, the INS_A (INS_B) voltage will drop to 1.4 V (1.6-0.2V) when the input power instantaneously drops to zero,
and will increase to 2.2V (1.6+0.2*3) when the input power instantaneously increases to 4 times the average power.
With lower V_TGT values the scaling factor also decreases, allowing INS_A (INS_B) to linearly track larger swings of input
power.
iPAR Output & Input RF Signal Envelope
vs. Time for an Input Crest Factor of
9.03 dB @ 1900 MHz ^[2]
2.25
1.5
IPAR Output
INS [A,B] Output vs. Instantaneous
Input Power (Normalized to Average
Power)
3
IPWR(t) = (VTGT/10)x(Pin(t)/Pavg)+(1.6-(Vtgt/10))
2.8
1.75
1
2.6
2.4
1.25
0.5
2.2
0.75
0
0.25
-0.5
Input RF Signal Envelope
0
1
2
3
4
5
Time (usec)
2
1.8
1.6
1.4
0
=Pin/Pav*0.2+(1.6-0.2)
IPWR Output VTGT = 2V
=Pin/Pav*0.1+(1.6-0.1)
IPWR Output VTGT = 1V
2
4
6
8
10
12
INSTANTANEOUS INPUT POWER
(NORMALIZED TO AVERAGE POWER)
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20 Alpha Road, Chelmsford, MA 01824 Phone: [phone] Fax: [phone]
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