Driver to drive?

[rickman]

On 11/4/2014 6:29 PM, rickman wrote:

I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I had found one op amp that might get me in the ballpark of power
consumption and I did some spice simulation on it. The current ends up
being in the 50 uA range which is more than I would like and the gain is
only around 100 before the bandwidth limits are felt which is less than
I would like. At 50 uA there is not the power to add a second stage.

Instead I was looking at some JFETs and found one I like, BF862 made by
NXP. I can construct a stage that gives a gain of 40 dB at only a
handful of uA. But when I try to cascade a second stage I have trouble.

The input capacitance is stated in the data sheet to be in the range of
10 pF. If I add a 10 pF cap to the output of the first stage I get
close to 40 dB of gain at the frequency of interest, 60 kHz. But when a
second stage is added with capacitive coupling the gain of the first
stage drops to 19 dB at 60 kHz while maintaining 40 dB at 1 kHz.

As a simple test, I put a capacitor in series with the gate and drove it
from a voltage source. I found the gate was at about half the voltage
of the voltage source when the capacitor was 300 pF. That says to me
the JFET model has 300 pF of capacitance. That just doesn't sound right.

I have seen other oddities from trying to drive the input of this part.
I have it biased correctly so the gate is not conducting. Any
suggestions? I am including the LTspice files below. I found one
thread on an audio web site where someone "improved" the model file.

Model file - spice_BF862.prm - put in "Simulations" directory below
schematic location
*******************
* BF862 SPICE MODEL MARCH 2007 NXP SEMICONDUCTORS
* ENVELOPE SOT23
* JBF862: 1, Drain, 2,Gate, 3,Source
Ld 1 4 L= 1.1nH
Ls 3 6 L= 1.25nH
Lg 2 5 L= 0.78nH
Rg 5 7 R= 0.535 Ohm
Cds 1 3 C= 0.0001pF
Cgs 2 3 C= 1.05pF
Cgd 1 2 C= 0.201pF
Co 4 6 C= 0.35092pF
JBF862 model parameters:
..model JBF862 NJF(Beta=47.800E-3 Betatce=-.5 Rd=.8 Rs=7.5000
Lambda=37.300E-3 Vto=-.57093
+ Vtotc=-2.0000E-3 Is=424.60E-12 Isr=2.995p N=1 Nr=2 Xti=3 Alpha=-1.0000E-3
+ Vk=59.97 Cgd=7.4002E-12 M=.6015 Pb=.5 Fc=.5 Cgs=8.2890E-12 Kf=87.5E-18
+ Af=1)
ENDS BF862


Schematic file - LowPowerPreAmp_JFET.asc
*******************
Version 4
SHEET 1 1340 680
WIRE 32 -128 -16 -128
WIRE 128 -128 32 -128
WIRE 368 -128 368 -160
WIRE 1008 -128 1008 -160
WIRE 128 -112 128 -128
WIRE -16 -96 -16 -128
WIRE -16 0 -16 -16
WIRE 128 0 128 -48
WIRE 368 0 368 -48
WIRE 416 0 368 0
WIRE 448 0 416 0
WIRE 608 0 512 0
WIRE 768 0 608 0
WIRE 1008 0 1008 -48
WIRE 1152 0 1008 0
WIRE 1264 0 1152 0
WIRE 368 32 368 0
WIRE 1008 32 1008 0
WIRE 1264 48 1264 0
WIRE 240 96 -16 96
WIRE 320 96 240 96
WIRE 768 96 768 0
WIRE 832 96 768 96
WIRE 960 96 832 96
WIRE 240 144 240 96
WIRE 368 144 368 128
WIRE 448 144 368 144
WIRE 496 144 448 144
WIRE 1008 144 1008 128
WIRE 1088 144 1008 144
WIRE 1136 144 1088 144
WIRE -16 160 -16 96
WIRE 768 160 768 96
WIRE 368 176 368 144
WIRE 1008 176 1008 144
WIRE 496 192 496 144
WIRE 1136 192 1136 144
WIRE 1264 224 1264 112
WIRE 240 256 240 224
WIRE -16 288 -16 240
WIRE 368 288 368 256
WIRE 496 288 496 256
WIRE 496 288 368 288
WIRE 1008 288 1008 256
WIRE 1136 288 1136 256
WIRE 1136 288 1008 288
WIRE 368 336 368 288
WIRE 768 336 768 240
WIRE 1008 336 1008 288
FLAG 368 336 0
FLAG -16 0 0
FLAG 32 -128 V2.2
FLAG -16 96 Vin
FLAG 240 256 0
FLAG -16 288 0
FLAG 128 0 0
FLAG 368 -160 V2.2
FLAG 448 144 Vs
FLAG 1008 336 0
FLAG 1152 0 Vout
FLAG 1008 -160 V2.2
FLAG 1088 144 Vs2
FLAG 768 336 0
FLAG 416 0 G1
FLAG 608 0 Vin2
FLAG 832 96 Vin3
FLAG 1264 224 0
SYMBOL voltage -16 -112 R0
WINDOW 123 0 0 Left 2
WINDOW 39 24 124 Left 2
SYMATTR InstName V1
SYMATTR Value 2.2v
SYMATTR SpiceLine Rser=1
SYMBOL voltage -16 144 R0
WINDOW 123 24 152 Left 2
WINDOW 39 24 124 Left 2
SYMATTR InstName V2
SYMATTR Value SINE(0 50uV 60K)
SYMATTR Value2 AC 1
SYMATTR SpiceLine Rser=10
SYMBOL res 224 128 R0
SYMATTR InstName R1
SYMATTR Value 10Meg
SYMBOL cap 112 -112 R0
SYMATTR InstName C5
SYMATTR Value 100ľF
SYMBOL res 352 -144 R0
SYMATTR InstName R3
SYMATTR Value 100k
SYMBOL njf 320 32 R0
SYMATTR InstName T1
SYMATTR Value JBF862
SYMBOL res 352 160 R0
SYMATTR InstName R2
SYMATTR Value 100k
SYMBOL cap 480 192 R0
SYMATTR InstName C1
SYMATTR Value 10ľF
SYMBOL res 992 -144 R0
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL njf 960 32 R0
SYMATTR InstName T2
SYMATTR Value JBF862
SYMBOL res 992 160 R0
SYMATTR InstName R5
SYMATTR Value 100k
SYMBOL cap 1120 192 R0
SYMATTR InstName C3
SYMATTR Value 1000nf
SYMBOL cap 448 16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C2
SYMATTR Value 10ľF
SYMBOL res 752 144 R0
SYMATTR InstName R4
SYMATTR Value 10Meg
SYMBOL cap 1248 48 R0
SYMATTR InstName C4
SYMATTR Value 10pF
TEXT 502 -200 Left 2 !.ac dec 10 0.1 10Meg
TEXT -24 400 Left 2 !.lib Simulations\\spice_BF862.prm

--

Rick

 

On Sat, 15 Nov 2014 22:17:38 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I haven't seen the original post, but are you building some type of
clock receiver ? Those work for a year with a single battery.

What kind of antenna are you using ? Do you really need a preamp ?

Do you have room for a tank circuit (L/C) on the collector/drain ?

 

[rickman]

On 11/16/2014 3:18 AM, upsidedown@downunder.com wrote:

On Sat, 15 Nov 2014 22:17:38 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I haven't seen the original post, but are you building some type of
clock receiver ? Those work for a year with a single battery.

Yes, it is a radio controlled clock.


> What kind of antenna are you using ? Do you really need a preamp ?

I was planning on a loop antenna made from RG6 cable, but if I have to
add an amplifier I may use a ferrite loop.


> Do you have room for a tank circuit (L/C) on the collector/drain ?

Room should not be a problem. But what is the point of a tank?

--

Rick

 

On Sun, 16 Nov 2014 03:47:44 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/16/2014 3:18 AM, upsidedown@downunder.com wrote:
On Sat, 15 Nov 2014 22:17:38 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I haven't seen the original post, but are you building some type of
clock receiver ? Those work for a year with a single battery.

Yes, it is a radio controlled clock.


What kind of antenna are you using ? Do you really need a preamp ?

I was planning on a loop antenna made from RG6 cable, but if I have to
add an amplifier I may use a ferrite loop.

Are you going to use a big (several meters) loop with the RG-6 center
conductor as a loop and cutting the shield at the top and using the
rest of the cable shield as a grounded static shield and using a small
coupling loop into the receiver ? With the main loop resonated by a
capacitor to 60 kHz, you should get quite decent signal without
preamplifier.

For anything smaller, a 5 cm ferrite bar is quite adequate due to the
high band noise, even if the ferrite antenna gain might be -40 dBi or
even -60 dBi.

Do you have room for a tank circuit (L/C) on the collector/drain ?

Room should not be a problem. But what is the point of a tank?

1. if you do not have a frequency selective antenna, this tank circuit
will provide the selectivity. Since this stage has a low gain at
unwanted frequencies, this reduces the risk of IP3 distortion, which
becomes critical at low collector/drain currents.

2. you get at least twice the voltage swing compared to the battery
voltage. Tapping the inductor or capacitor chain will provide nice
impedance matching avoiding the need for a cascaded stage.

 

On Sunday, November 16, 2014 10:33:27 AM UTC-5, upsid...@downunder.com wrote:

On Sun, 16 Nov 2014 06:03:03 -0700, RobertMacy
robert.a.macy@gmail.com> wrote:

On Sun, 16 Nov 2014 05:49:41 -0700, RobertMacy <robert.a.macy@gmail.com
wrote:

...snip.....
Third, take a VERY close look at using a micro power PIC, or such. Timex
watches are something like 10kHz clock speed? But at 60kHz, you should
be at least 120kHz clock, or maybe 4X that, or such. And, then use
'synchronous' detection, essentially creating a tone specific FFT. Some
simple program like run an accumulator as +/- AT 60kHz.

arrrrgggg! that should have read,
...run an accumulator as +/- AT 120kS/s.

Those time stations typically transmit on/off keying, so putting a
rectifier after the resonant circuit will generate a varying DC, which
needs to be sampled only a few times a second for a time display
resolution of 1 s.

If better accuracy is needed, then it might make sense to actually
phase lock to the 60 kHz carrier and get accuracy in the order of tens
of microseconds.

Not anymore:

http://www.nist.gov/pml/div688/grp40/upload/NIST-Enhanced-WWVB-Broadcast-Format-sept-2012-Radio-Station-staff.pdf

Receiver Q of 6000 is typical.

 

[RobertMacy]

On Sun, 16 Nov 2014 01:47:44 -0700, rickman <gnuarm@gmail.com> wrote:

On 11/16/2014 3:18 AM, upsidedown@downunder.com wrote:
On Sat, 15 Nov 2014 22:17:38 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption
to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I haven't seen the original post, but are you building some type of
clock receiver ? Those work for a year with a single battery.

Yes, it is a radio controlled clock.


What kind of antenna are you using ? Do you really need a preamp ?

I was planning on a loop antenna made from RG6 cable, but if I have to
add an amplifier I may use a ferrite loop.


Do you have room for a tank circuit (L/C) on the collector/drain ?

Room should not be a problem. But what is the point of a tank?

First, use the L/C circuit tuned near 60kHz with at least Q of 100 as a
'pre-filter'. It will kill AC mains and any higher frequencies, like AM
radio stations.
Second, if this is a 'radio receiver' that receives magnetic fields; go
ahead and use the ferrite approach. That will essentiall 'suck' in the
fields, make a smaller coil look like it's subtending a much larger area,
but just like an air core loop, it will be 'vector' sensitive, meaning at
certian orientations - no signal.
Third, take a VERY close look at using a micro power PIC, or such. Timex
watches are something like 10kHz clock speed? But at 60kHz, you should be
at least 120kHz clock, or maybe 4X that, or such. And, then use
'synchronous' detection, essentially creating a tone specific FFT. Some
simple program like run an accumulator as +/- AT 60kHz.

Why resonant antenna? You can gain significantly voltage coming in.
Envision the generated voltage creating N*2piFB*Area will be small, but
put in a tank with Q=100 and the signals start flying around 100X bigger,
higher impedance but this is low frequency voltage. Tapping off the
parallel resonance you just gained 100X in the incoming voltage. Now you
need more like a buffer than a gain stage.

Note, I'm an Analog Designer from waaaay back, but sometimes going
straight to digital has its advantages.

 

[RobertMacy]

On Sun, 16 Nov 2014 05:49:41 -0700, RobertMacy <robert.a.macy@gmail.com>
wrote:

...snip.....
Third, take a VERY close look at using a micro power PIC, or such. Timex
watches are something like 10kHz clock speed? But at 60kHz, you should
be at least 120kHz clock, or maybe 4X that, or such. And, then use
'synchronous' detection, essentially creating a tone specific FFT. Some
simple program like run an accumulator as +/- AT 60kHz.

arrrrgggg! that should have read,
...run an accumulator as +/- AT 120kS/s.

 

On Sunday, November 16, 2014 3:18:04 AM UTC-5, upsid...@downunder.com wrote:

On Sat, 15 Nov 2014 22:17:38 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I haven't seen the original post, but are you building some type of
clock receiver ? Those work for a year with a single battery.

Right, but they are mostly IC receivers with a shutdown feature which knocks them down into 0.1 uA current drain territory. When they're up and running, the drain is in the 100uA region. So the trick to long battery life is a shutdown/ programmed wakeup operation.

 

On Sun, 16 Nov 2014 06:03:03 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:

On Sun, 16 Nov 2014 05:49:41 -0700, RobertMacy <robert.a.macy@gmail.com
wrote:

...snip.....
Third, take a VERY close look at using a micro power PIC, or such. Timex
watches are something like 10kHz clock speed? But at 60kHz, you should
be at least 120kHz clock, or maybe 4X that, or such. And, then use
'synchronous' detection, essentially creating a tone specific FFT. Some
simple program like run an accumulator as +/- AT 60kHz.

arrrrgggg! that should have read,
...run an accumulator as +/- AT 120kS/s.

Those time stations typically transmit on/off keying, so putting a
rectifier after the resonant circuit will generate a varying DC, which
needs to be sampled only a few times a second for a time display
resolution of 1 s.

If better accuracy is needed, then it might make sense to actually
phase lock to the 60 kHz carrier and get accuracy in the order of tens
of microseconds.

 

[Joerg]

rickman wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I had found one op amp that might get me in the ballpark of power
consumption and I did some spice simulation on it. The current ends up
being in the 50 uA range which is more than I would like and the gain is
only around 100 before the bandwidth limits are felt which is less than
I would like. At 50 uA there is not the power to add a second stage.

Instead I was looking at some JFETs and found one I like, BF862 made by
NXP. I can construct a stage that gives a gain of 40 dB at only a
handful of uA. But when I try to cascade a second stage I have trouble.

The input capacitance is stated in the data sheet to be in the range of
10 pF. If I add a 10 pF cap to the output of the first stage I get
close to 40 dB of gain at the frequency of interest, 60 kHz. But when a
second stage is added with capacitive coupling the gain of the first
stage drops to 19 dB at 60 kHz while maintaining 40 dB at 1 kHz.

You need a FET with an input capacitance an order of magnitude lower.
Got to run now and can't find it so quickly but ask John Larkin. He
suggested a FET a while ago that is IIRC under 1pF.

Dual gate FETs are another option. An example, although this one still
has 2pF at gate 1:

http://www.nxp.com/documents/data_sheet/BF998.pdf

Have you tried BJTs? Only sad thing is, many of the very low power
Japanese ones have been discontinued.

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

 

[whit3rd]

On Saturday, November 15, 2014 7:18:17 PM UTC-8, rickman wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing.

How about a programmable-bias-current op amp? LM4250 is easily
available, there used to be lots of others. OTAs like LM13700 have similar
low-power specifications, with the additional feature that output loads
don't change the power requirement.

 

[John Larkin]

On Sun, 16 Nov 2014 08:14:11 -0800, Joerg <news@analogconsultants.com>
wrote:

rickman wrote:
On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I had found one op amp that might get me in the ballpark of power
consumption and I did some spice simulation on it. The current ends up
being in the 50 uA range which is more than I would like and the gain is
only around 100 before the bandwidth limits are felt which is less than
I would like. At 50 uA there is not the power to add a second stage.

Instead I was looking at some JFETs and found one I like, BF862 made by
NXP. I can construct a stage that gives a gain of 40 dB at only a
handful of uA. But when I try to cascade a second stage I have trouble.

The input capacitance is stated in the data sheet to be in the range of
10 pF. If I add a 10 pF cap to the output of the first stage I get
close to 40 dB of gain at the frequency of interest, 60 kHz. But when a
second stage is added with capacitive coupling the gain of the first
stage drops to 19 dB at 60 kHz while maintaining 40 dB at 1 kHz.


You need a FET with an input capacitance an order of magnitude lower.
Got to run now and can't find it so quickly but ask John Larkin. He
suggested a FET a while ago that is IIRC under 1pF.

NE3509 maybe... a bit under 1 pF. Phemts have high 1/f noise corners,
so I don't know how well they might work at 60 KHz and low current.
Phil probably has lf noise data on a Skyworks part.

The key to low-noise, low-power gain in narrowband amps is proper
input network tuning. A tuned circuit makes voltage gain for zero
power consumption. Ditto interstage coupling. This problem may not
actually need a super-low-capacitance part.



--

John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[rickman]

On 11/16/2014 5:08 AM, upsidedown@downunder.com wrote:

On Sun, 16 Nov 2014 03:47:44 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/16/2014 3:18 AM, upsidedown@downunder.com wrote:
On Sat, 15 Nov 2014 22:17:38 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I haven't seen the original post, but are you building some type of
clock receiver ? Those work for a year with a single battery.

Yes, it is a radio controlled clock.


What kind of antenna are you using ? Do you really need a preamp ?

I was planning on a loop antenna made from RG6 cable, but if I have to
add an amplifier I may use a ferrite loop.

Are you going to use a big (several meters) loop with the RG-6 center
conductor as a loop and cutting the shield at the top and using the
rest of the cable shield as a grounded static shield and using a small
coupling loop into the receiver ? With the main loop resonated by a
capacitor to 60 kHz, you should get quite decent signal without
preamplifier.

That's the general idea but in an 8 turn 2 foot loop. I may add another
50 foot of RG6 (helps with the split) to boost the signal further.
"Decent" must be defined. This signal is not so strong, 100 uV/m and
this loop will only give 26 uV counting a Q of 90 which might not fully
materialize by the time it is plugged into the receiver.

As I think about this (I do more thinking than designing sometimes) I am
becoming less and less convinced I can do this without a preamp.

For anything smaller, a 5 cm ferrite bar is quite adequate due to the
high band noise, even if the ferrite antenna gain might be -40 dBi or
even -60 dBi.

Not sure why you would compare the ferrite antenna to an isotropic
antenna, but when compared to the 2 foot loop the equations show the 2
foot loop provides a stronger signal. Now that I am considering a
preamp I may return to the idea of the ferrite loop antenna. Lol, if I
do that I can explore the joys of Litz wire.

Do you have room for a tank circuit (L/C) on the collector/drain ?

Room should not be a problem. But what is the point of a tank?

1. if you do not have a frequency selective antenna, this tank circuit
will provide the selectivity. Since this stage has a low gain at
unwanted frequencies, this reduces the risk of IP3 distortion, which
becomes critical at low collector/drain currents.

The antenna is already highly tuned to the frequency of interest.
Unlike voice broadcasts the bandwidth of this signal is just double
digit Hz so a Q as high as feasible is useful. That is why RG6 was
picked, with a center conductor that pushes the skin effect the Q will
be as good as practical (without using Litz wire, lol).

2. you get at least twice the voltage swing compared to the battery
voltage. Tapping the inductor or capacitor chain will provide nice
impedance matching avoiding the need for a cascaded stage.

Impedance matching to what? My "receiver" is an FPGA with a rather high
impedance input, measured in Megaohms in parallel with single digit pF.

I don't need to worry about Vcc (or Vdd) limiting voltage swing even
with the amp the voltage is low. If the tuned circuit will boost the
voltage otherwise I would consider it. Would a tank circuit be put in
series with a resistance? Otherwise how is the DC point established? I
am using a source resistor with bypass cap to bias the gate-source
voltage (reminds me of tube circuits) but a resistor is also needed in
the drain connection, no?

--

Rick

 

[rickman]

On 11/16/2014 1:54 PM, John Larkin wrote:

On Sun, 16 Nov 2014 08:14:11 -0800, Joerg <news@analogconsultants.com
wrote:

rickman wrote:
On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I had found one op amp that might get me in the ballpark of power
consumption and I did some spice simulation on it. The current ends up
being in the 50 uA range which is more than I would like and the gain is
only around 100 before the bandwidth limits are felt which is less than
I would like. At 50 uA there is not the power to add a second stage.

Instead I was looking at some JFETs and found one I like, BF862 made by
NXP. I can construct a stage that gives a gain of 40 dB at only a
handful of uA. But when I try to cascade a second stage I have trouble.

The input capacitance is stated in the data sheet to be in the range of
10 pF. If I add a 10 pF cap to the output of the first stage I get
close to 40 dB of gain at the frequency of interest, 60 kHz. But when a
second stage is added with capacitive coupling the gain of the first
stage drops to 19 dB at 60 kHz while maintaining 40 dB at 1 kHz.


You need a FET with an input capacitance an order of magnitude lower.
Got to run now and can't find it so quickly but ask John Larkin. He
suggested a FET a while ago that is IIRC under 1pF.

NE3509 maybe... a bit under 1 pF. Phemts have high 1/f noise corners,
so I don't know how well they might work at 60 KHz and low current.
Phil probably has lf noise data on a Skyworks part.

The key to low-noise, low-power gain in narrowband amps is proper
input network tuning. A tuned circuit makes voltage gain for zero
power consumption. Ditto interstage coupling. This problem may not
actually need a super-low-capacitance part.

Thanks for the suggestion. Noise shouldn't be a problem in this app.
The noise is typically dominated by terrestrial sources of interference.
The antenna has a Q of 90 but the signal is still very low level.

The thing I don't get is that the BF862 data sheet says the gate source
capacitance is in the 10 pF ballpark. But in the simulation it seems to
be more like 300 pF. The frequency response curves don't look anything
like capacitive loading either. Is this some strange non-linear thing
because I am using the part with a very low drain current ~5 uA?

Someone here pointed out to me once that at low collector currents the
gain falls off. That didn't make a lot of sense until just now I was
looking at the ID vs VG1 of the BBF998 and I realized how it is like a
leaky faucet. You can easily change the flow rate from 1 gal/min to 1.1
gal/min. But trying to change it from 1 drop per minute to 1.1 drop per
minute is not so easy. The curve is asymptotic to the X axis making it
very hard to get much change in current as it approaches 0.

--

Rick

 

[rickman]

On 11/16/2014 7:49 AM, RobertMacy wrote:

On Sun, 16 Nov 2014 01:47:44 -0700, rickman <gnuarm@gmail.com> wrote:

On 11/16/2014 3:18 AM, upsidedown@downunder.com wrote:
On Sat, 15 Nov 2014 22:17:38 -0500, rickman <gnuarm@gmail.com> wrote:

On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power
consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I haven't seen the original post, but are you building some type of
clock receiver ? Those work for a year with a single battery.

Yes, it is a radio controlled clock.


What kind of antenna are you using ? Do you really need a preamp ?

I was planning on a loop antenna made from RG6 cable, but if I have to
add an amplifier I may use a ferrite loop.


Do you have room for a tank circuit (L/C) on the collector/drain ?

Room should not be a problem. But what is the point of a tank?


First, use the L/C circuit tuned near 60kHz with at least Q of 100 as a
'pre-filter'. It will kill AC mains and any higher frequencies, like AM
radio stations.
Second, if this is a 'radio receiver' that receives magnetic fields; go
ahead and use the ferrite approach. That will essentiall 'suck' in the
fields, make a smaller coil look like it's subtending a much larger
area, but just like an air core loop, it will be 'vector' sensitive,
meaning at certian orientations - no signal.

The equations I have for loop antenna show a large coil air core will
give a greater voltage than a small ferrite core. Of course the devil
is in the details, but I think this is true for most "reasonable"
parameters. The mu of the ferrite is only single digit and so has a
limited improvement on the gain of the antenna. Number of turns has a
linear impact while the radius has a squared effect. Ferrites are
mostly used where space is at a premium.

Third, take a VERY close look at using a micro power PIC, or such. Timex
watches are something like 10kHz clock speed? But at 60kHz, you should
be at least 120kHz clock, or maybe 4X that, or such. And, then use
'synchronous' detection, essentially creating a tone specific FFT. Some
simple program like run an accumulator as +/- AT 60kHz.

I'm all over the digital aspects of this. But it turns out that is the
*easy* part. lol Just finding *a* equation for inductance was an
education. Turns out unlike capacitance which is pretty simple, the
formula for inductance are very messy and plentiful.

Why resonant antenna? You can gain significantly voltage coming in.
Envision the generated voltage creating N*2piFB*Area will be small, but
put in a tank with Q=100 and the signals start flying around 100X
bigger, higher impedance but this is low frequency voltage. Tapping off
the parallel resonance you just gained 100X in the incoming voltage. Now
you need more like a buffer than a gain stage.

Note, I'm an Analog Designer from waaaay back, but sometimes going
straight to digital has its advantages.

That was what I had hoped to show with this project. I envisioned it
two years ago I believe, but put it aside and have only given it a
little thought since then.

The comment was about a tuned circuit in the drain leg of an amplifier
stage. The antenna is already tuned and the calculated Q is 90.

--

Rick

 

[rickman]

On 11/16/2014 10:33 AM, upsidedown@downunder.com wrote:

On Sun, 16 Nov 2014 06:03:03 -0700, RobertMacy
robert.a.macy@gmail.com> wrote:

On Sun, 16 Nov 2014 05:49:41 -0700, RobertMacy <robert.a.macy@gmail.com
wrote:

...snip.....
Third, take a VERY close look at using a micro power PIC, or such. Timex
watches are something like 10kHz clock speed? But at 60kHz, you should
be at least 120kHz clock, or maybe 4X that, or such. And, then use
'synchronous' detection, essentially creating a tone specific FFT. Some
simple program like run an accumulator as +/- AT 60kHz.

arrrrgggg! that should have read,
...run an accumulator as +/- AT 120kS/s.

Those time stations typically transmit on/off keying, so putting a
rectifier after the resonant circuit will generate a varying DC, which
needs to be sampled only a few times a second for a time display
resolution of 1 s.

If better accuracy is needed, then it might make sense to actually
phase lock to the 60 kHz carrier and get accuracy in the order of tens
of microseconds.

That's assuming you can *see* the carrier. My plan is to dig the signal
out of the noise with a long term averager, not unlike a DFT bin or you
might call it a lock-in amplifier. I am told the phase modulation is
easier to dig out than the AM signal. We will see.

--

Rick

 

[rickman]

On 11/16/2014 11:14 AM, Joerg wrote:

rickman wrote:
On 11/4/2014 6:29 PM, rickman wrote:
I am working on a project for receiving a very narrow bandwidth signal
at 60 kHz. One of the design goals is to keep the power consumption to
an absolute minimum. I'm trying to figure out how to run a
pre-amplifier on less than 100 uW. So far I have found nothing. Any
suggestions?

I had found one op amp that might get me in the ballpark of power
consumption and I did some spice simulation on it. The current ends up
being in the 50 uA range which is more than I would like and the gain is
only around 100 before the bandwidth limits are felt which is less than
I would like. At 50 uA there is not the power to add a second stage.

Instead I was looking at some JFETs and found one I like, BF862 made by
NXP. I can construct a stage that gives a gain of 40 dB at only a
handful of uA. But when I try to cascade a second stage I have trouble.

The input capacitance is stated in the data sheet to be in the range of
10 pF. If I add a 10 pF cap to the output of the first stage I get
close to 40 dB of gain at the frequency of interest, 60 kHz. But when a
second stage is added with capacitive coupling the gain of the first
stage drops to 19 dB at 60 kHz while maintaining 40 dB at 1 kHz.


You need a FET with an input capacitance an order of magnitude lower.

Can you explain this? The info I have on the BF862 shows 10 pF range
gate to source. If I replace the FET gate with a 10 pF load on the
first stage the output looks normal. With the FET in place the
frequency response of the first stage output looks very bad with a
complex curve rather than just a simple capacitor loading.

Got to run now and can't find it so quickly but ask John Larkin. He
suggested a FET a while ago that is IIRC under 1pF.

Dual gate FETs are another option. An example, although this one still
has 2pF at gate 1:

http://www.nxp.com/documents/data_sheet/BF998.pdf

Have you tried BJTs? Only sad thing is, many of the very low power
Japanese ones have been discontinued.

I know nothing about dual gate FETs. The BJTs I have looked at won't
get the high input impedance or the low biasing currents I want. The
JFET is operating with about 5 uA of drain current.

--

Rick

 

[RobertMacy]

On Sun, 16 Nov 2014 14:01:55 -0700, rickman <gnuarm@gmail.com> wrote:

On 11/16/2014 7:49 AM, RobertMacy wrote:
On Sun, 16 Nov 2014 01:47:44 -0700, rickman <gnuarm@gmail.com> wrote:
...snip....
First, use the L/C circuit tuned near 60kHz with at least Q of 100 as a
'pre-filter'. It will kill AC mains and any higher frequencies, like AM
radio stations.
Second, if this is a 'radio receiver' that receives magnetic fields; go
ahead and use the ferrite approach. That will essentiall 'suck' in the
fields, make a smaller coil look like it's subtending a much larger
area, but just like an air core loop, it will be 'vector' sensitive,
meaning at certian orientations - no signal.

The equations I have for loop antenna show a large coil air core will
give a greater voltage than a small ferrite core. Of course the devil
is in the details, but I think this is true for most "reasonable"
parameters. The mu of the ferrite is only single digit and so has a
limited improvement on the gain of the antenna. Number of turns has a
linear impact while the radius has a squared effect. Ferrites are
mostly used where space is at a premium.

Get a copy of free femm 4.2 THEN you can get EXACT answers, including
expected volage in a free space field AND he losses caused by skin effect.

Third, take a VERY close look at using a micro power PIC, or such. Timex
watches are something like 10kHz clock speed? But at 60kHz, you should
be at least 120kHz clock, or maybe 4X that, or such. And, then use
'synchronous' detection, essentially creating a tone specific FFT. Some
simple program like run an accumulator as +/- AT 60kHz.

I'm all over the digital aspects of this. But it turns out that is the
*easy* part. lol Just finding *a* equation for inductance was an
education. Turns out unlike capacitance which is pretty simple, the
formula for inductance are very messy and plentiful.

I gave up years ago trying to apply 'cookbook' formulas, after being badly
burnt by poorly worded assumptions giving total way wrong answers. Again
femm 4.2 yields better than 1% even when sloppy.

...snip....
The comment was about a tuned circuit in the drain leg of an amplifier
stage. The antenna is already tuned and the calculated Q is 90.

but you still haven't posted schematic or models ? Everybody could help a
lot more given that and the Rx field assumptions etc.

 

[miso]

John Larkin wrote:

This is awful:
http://www.analog.com/static/imported-files/data_sheets/ADCMP567.pdf
It's still Rev 0, from 2003.
The only associated appnote is from 1989!

And specifically what is wrong?

 

On Sunday, November 16, 2014 7:49:04 PM UTC-8, jurb...@gmail.com wrote:
> I mean because if the defendant wins the case, the record should disappear.

What is the defendant's justification for illegally detaintaining the property for months or years pending trial? Winning the case does not change the fact he broke the law, and got away without much consequences. Yes, the court system is fuck up, idiot judges allow them to game the system. I, as a property owner, would avoid such renters at all cost. Actually, i would avoid all renters after this, leaving the property vacant is less of an headache.