Maker Pro
Maker Pro

Low Parts-Count Oscillators

T

Tim Wescott

Jan 1, 1970
0
I'm working on a small, battery powered receiver that I hope to keep
below 1/2 ounce total weight. I need to make a good VCO that will
operate from 100 to 150MHz on 2.7V to 5V with minimal parts count and
hopefully minimal BOM cost. Everything I've done so far has been from a
dependable 12V rail and the more components the better, so this low
voltage, low parts-count stuff is new territory.

At the moment I'm looking at a Colpitts with the base bias derived from
an LM385, and a single MMBV210x for tuning.


VCC
100 +
___ |
.-------o----------o----------o---|___|--'
| | | |
| .-. | |
--- | | C| ---
--- | |10k C| ---
| '-' C| |
| | | || |
=== | o----||----o
GND | | || |
| |/ |
o--------| |
| |> | 10k
| | | || ___ Vtune
\---\ o----------o---||----o----|___|-----o
LM385 /|\ | || |
| .-. ---
| | | ---
=== | | 1k /|\ MMBV210x
GND '-' |
| |
| |
=== ===
GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

I'm fairly confident that this will work, but it has an awful lot of
parts for this application. Any suggestions on how I can do better than
this?

Thanks.
 
M

Mike Engelhardt

Jan 1, 1970
0
Tim,
I'm working on a small, battery powered receiver that I hope to keep
below 1/2 ounce total weight. I need to make a good VCO that will
operate from 100 to 150MHz on 2.7V to 5V with minimal parts count and
hopefully minimal BOM cost. Everything I've done so far has been from a
dependable 12V rail and the more components the better, so this low
voltage, low parts-count stuff is new territory.

At the moment I'm looking at a Colpitts with the base bias derived from
an LM385, and a single MMBV210x for tuning.

You might be able to drop the part count by using a
an inductor with two windings. That counts as one
part. This version also uses a higher Z power feed,
so it might need less filtering. At higher frequencies,
another method uses gain element parasitic reactances
to complete the feedback network for a complete
oscialltor in just a few parts.

--Mike

6 part VCO LTspice schematic:

--- vco.asc ---
Version 4
SHEET 1 2624 2336
WIRE 2368 2000 2368 2016
WIRE 2368 2096 2368 2112
WIRE 2224 1920 2224 1904
WIRE 2224 1904 2368 1904
WIRE 2368 1920 2368 1904
WIRE 1936 1984 1936 2016
WIRE 2080 2096 2080 2080
WIRE 2080 2000 2080 1904
WIRE 2224 1904 2160 1904
WIRE 1936 1920 1936 1904
WIRE 1936 1904 2080 1904
WIRE 2096 1904 2080 1904
WIRE 2224 2016 2224 2096
WIRE 1936 2096 1936 2112
WIRE 1936 2016 1936 2032
WIRE 1936 2016 1904 2016
WIRE 1824 2016 1648 2016
WIRE 1648 2016 1648 2048
WIRE 1648 2128 1648 2176
WIRE 2176 1984 2144 1984
WIRE 2144 1984 2144 2000
WIRE 2144 2080 2144 2096
FLAG 2368 2112 GND
FLAG 2224 2096 GND
FLAG 1648 2176 0
FLAG 2144 2096 0
FLAG 1936 2112 0
FLAG 2080 2096 0
SYMBOL njf 2176 1920 R0
SYMATTR InstName J1
SYMATTR Value 2N5484
SYMBOL voltage 2368 2000 R0
SYMATTR InstName V1
SYMATTR Value 10.
SYMBOL cap 1920 1920 R0
SYMATTR InstName C4
SYMATTR Value 25p
SYMBOL ind2 2064 2096 M180
WINDOW 0 -11 80 Right 0
WINDOW 3 1 37 Right 0
SYMATTR InstName L1
SYMATTR Value 100µ
SYMBOL cap 2096 1920 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName C1
SYMATTR Value 3p
SYMBOL ind2 2160 1984 M0
WINDOW 0 -4 37 Right 0
WINDOW 3 -2 77 Right 0
SYMATTR InstName L2
SYMATTR Value 3µ
SYMBOL res 2352 1904 R0
SYMATTR InstName R1
SYMATTR Value 1K
SYMBOL varactor 1920 2096 M180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D1
SYMATTR Value MV2201
SYMATTR Type diode
SYMBOL res 1920 2000 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 100K
SYMBOL voltage 1648 2032 R0
WINDOW 3 11 110 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(3 20 0 1u 1u .5m 1m)
TEXT 1912 2248 Left 0 !.tran 1m startup
TEXT 2128 1840 Center 0 !K1 L1 L2 1.
 
M

Martin Farrell

Jan 1, 1970
0
Tim Wescott said:
I'm working on a small, battery powered receiver that I hope to keep
below 1/2 ounce total weight. I need to make a good VCO that will
operate from 100 to 150MHz on 2.7V to 5V with minimal parts count and
hopefully minimal BOM cost.
Tim,

This circuit works well at 184MHz with a BFT92 and a single cell. I've
tried it with NPN but it's not as well behaved. Most people don't
believe that shorting base to collector with the L will work - but it
does. Noise performance is a bit limited by the low Vswing on the L.
___
O-----------o------------|___|---------1.2 - 5V
| |
| .-.
| | |
| | | 470
| '-' ___
| | OUT o--|___|--Tune
| o-----o-----------o |
| | | | |
| | | Cb --- |
| | Ce | --- |
Cdc--- --- >| | || |
--- --- |---------o--o||--o
| | /| | || |
| | | | |
| | | C| ---
| | | C| L ---
| | | C| /\
| | | | |
o-----o-----o-----------o-------o
GND


created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
 
Top