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Entry  Fri May 6 01:27:12 2011, Koji, Summary, General, aLIGO BBPD / Green PD investigation PD_response.pdfFFD-100_AP389_MCL.pdf
    Reply  Sat May 7 12:57:54 2011, Koji, Summary, General, aLIGO BBPD / Green PD investigation PD_response.pdf
       Reply  Tue May 10 09:05:49 2011, Koji, Update, General, aLIGO BBPD / Green PD investigation PD_response.pdf
          Reply  Wed Jun 1 21:56:43 2011, Koji, Update, General, aLIGO BBPD / Green PD final result PD_response.pdflinearity_GALI_6.pdf
Message ID: 4658     Entry time: Sat May 7 12:57:54 2011     In reply to: 4649     Reply to this: 4676
Author: Koji 
Type: Summary 
Category: General 
Subject: aLIGO BBPD / Green PD investigation 

The RF amplifier of the prototype BBPD has been replaced from ERA-5SM to MAR-6SM.
The bandwidth is kept (~200MHz for S3399 with 30V_bias), and the noise level got better
while the maximum handling power was reduced.

MAR-6SM is a monolithic amplifier from Minicircuits. It is similar to ERA-5SM but has lower noise
and the lower output power.

AP389 ERA-5 MAR-6
Freq Range 10-250MHz DC-4GHz DC-2GHz
Gain >24.5dB 20dBtyp 21.8dBtyp
Output power (1dB comp.)
+23dBm +18.4dBm +3.7dBm
IP3 36dBm 33dBm 18.1dBm
Noise Figure <3.3dB 3.5dB 2.3dB

The noise floor corresponds to the shotnoise of the 0.4mA DC current.
Now the mess below 50MHz and between 90-110MHz should be cleaned up.
They are consistently present no matter how I change the PD/RF amp (ERA<->MAR)/bias voltage.

I should test the circuit with a different board and enhanced power/bias supply bypassing.

Discussion on the RF power (with M. Evans)

- Assume 5mA is the maximum RF (~50mW for 1064nm, ~15mW for 532nm). This is already plenty in terms of the amount of the light.

- 100% intenisty modulation for 5mA across 50Ohm induces -2dBm RF power input for the amplifier.

- Assume if we use MAR-6 for the preamplifier. The max input power is about -18dBm.
  This corresponds to 16% intensity modulation. It may be OK, if we have too strong intensity modulation, we can limit the power
  down to 0.8mA in the worst case. The shot noise will still be above the noise level.

- In the most of the applications, the RF power is rather small. (i.e. 40m green beat note would expected to be -31dBm on the RF amp input at the higherst, -50dBm in practice)
So probably we need more gain. If we can add 10-12dB more gain, that would be useful.

- What is the requirement for the power amplifier?

  • Gain: 10~12dB
  • Output (1dBcomp): +3dBm +Gain (13dBm~15dBm)
  • Noise level / Noise Figure: 3nV/rtHz or NF=14dB
    The output of MAR-6 has the votage level of ~7nV/rtHz. If we bring the power amplifier with input noise of ~3nV/rtHz,
    we can surppress the degradation of the input equivalent noise to the level of 10%. This corresponds to N.F. of 14dB.

Search result for Freq Range 10-200MHz / Max Gain 14dB / Max NF 15dB / Min Power Out 13dBm
GVA-81 is available at the 40m. ERA-4SM, ERA-6SM, HELA-10D are available at Downs.

Model Name Frequency [MHz] DC Power Case Style Price
Low High Current [mA] Volt [V]
ERA-4 DC 4000 65 4.5 VV105
ERA-4SM DC 4000 65 4.5 WW107
ERA-4XSM DC 4000 65 4.5 WW107
ERA-6 DC 4000 70 5 VV105
ERA-6SM DC 4000 70 5 WW107
GALI-6 DC 4000 70 5 DF782
GVA-81+ DC 7000 112 5 DF782
HELA-10C 5 450 525 12 CM624
HELA-10D 8 300 525 12 CM624

Freq Range DC-6GHz DC-4GHz DC-4GHz DC-4GHz
Gain 10.5dB 13.7dB 12.6dB 12.2dB
Output power (1dB comp.)
+19dBm +17.5dBm +17.1dBm +18.2dBm
IP3 42dBm 36dBm 36.5dBm 35.5dBm
Noise Figure 7.3dB 4dB 4.4dB 4.5dB


Conversion between nV/rtHz and NF (in the 50Ohm system)

SN1: Connect signal source (50Ohm output) to a 50Ohm load.
Power ratio between the noise and the signal

SN1 = (4 k T (R/2)) / (S/2)^2

SN2: Connect signal source (50Ohm output) to an RF amp.
Only the voltage noise was considered.

SN2 = (4 k T (R/2) + Vn^2) / (S/2)^2

10 Log10(SN2/SN1) = 10. Log10(1 + 2.42 (Vn / 1nVrtHz)^2)

Vn: 0 nVrtHz ==> 0dB
Vn: 0.5 nVrtHz ==> 2dB
Vn: 1 nVrtHz ==> 5dB
Vn: 2 nVrtHz ==> 10dB
Vn: 3 nVrtHz ==> 13.5dB

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