DATA SHEET
Product specification
Supersedes data of April 1995
File under Discrete Semiconductors, SC07
1996 Jul 30
DISCRETE SEMICONDUCTORS
BF908; BF908R
Dual-gate MOS-FETs
1996 Jul 30
2
Philips Semiconductors
Product specification
Dual-gate MOS-FETs
BF908; BF908R
FEATURES
High forward transfer admittance
Short channel transistor with high forward transfer
admittance to input capacitance ratio
Low noise gain controlled amplifier up to 1 GHz.
APPLICATIONS
VHF and UHF applications with 12 V supply voltage,
such as television tuners and professional
communications equipment.
DESCRIPTION
Depletion type field-effect transistor in a plastic
microminiature SOT143 or SOT143R package. The
transistors are protected against excessive input voltage
surges by integrated back-to-back diodes between gates
and source.
PINNING
CAUTION
The device is supplied in an antistatic package. The
gate-source input must be protected against static
discharge during transport or handling.
PIN
SYMBOL
DESCRIPTION
1
s, b
source
2
d
drain
3
g
2
gate 2
4
g
1
gate 1
Fig.1
Simplified outline (SOT143) and
symbol; BF908.
handbook, halfpage
s,b
d
g
1
g
2
4
3
2
1
Top view
MAM039
Fig.2
Simplified outline (SOT143R) and
symbol; BF908R.
handbook, halfpage
s,b
d
g
1
g
2
MAM040
3
4
1
2
Top view
QUICK REFERENCE DATA
SYMBOL
PARAMETER
CONDITIONS
MIN.
TYP.
MAX.
UNIT
V
DS
drain-source voltage
-
-
12
V
I
D
drain current
-
-
40
mA
P
tot
total power dissipation
-
-
200
mW
T
j
operating junction temperature
-
-
150
C
y
fs
forward transfer admittance
36
43
50
mS
C
ig1-s
input capacitance at gate 1
2.4
3.1
4
pF
C
rs
reverse transfer capacitance
f = 1 MHz
20
30
45
pF
F
noise figure
f = 800 MHz
-
1.5
2.5
dB
1996 Jul 30
3
Philips Semiconductors
Product specification
Dual-gate MOS-FETs
BF908; BF908R
LIMITING VALUES
In accordance with the Absolute Maximum Rating System (IEC 134).
Note
1. Device mounted on a printed-circuit board.
SYMBOL
PARAMETER
CONDITIONS
MIN.
MAX.
UNIT
V
DS
drain-source voltage
-
12
V
I
D
drain current
-
40
mA
I
G1
gate 1 current
-
10
mA
I
G2
gate 2 current
-
10
mA
P
tot
total power dissipation
see Fig.3; note 1
BF908
up to T
amb
= 50
C
-
200
mW
BF908R
up to T
amb
= 40
C
-
200
mW
T
stg
storage temperature
-
65
+150
C
T
j
operating junction temperature
-
150
C
Fig.3 Power derating curves.
handbook, halfpage
0
50
100
150
200
250
0
50
100
150
200
BF908
BF908R
P
tot
(mW)
Tamb ( C)
o
MRC275
1996 Jul 30
4
Philips Semiconductors
Product specification
Dual-gate MOS-FETs
BF908; BF908R
THERMAL CHARACTERISTICS
Note
1. Device mounted on a printed-circuit board.
STATIC CHARACTERISTICS
T
j
= 25
C; unless otherwise specified.
DYNAMIC CHARACTERISTICS
Common source; T
amb
= 25
C; V
DS
= 8 V; V
G2-S
= 4 V; I
D
= 15 mA; unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
VALUE
UNIT
R
th j-a
thermal resistance from junction to ambient
note 1
BF908
500
K/W
BF908R
550
K/W
SYMBOL
PARAMETER
CONDITIONS
MIN.
TYP.
MAX.
UNIT
V
(BR)G1-SS
gate 1-source breakdown voltage
V
G2-S
= V
DS
= 0; I
G1-S
= 10 mA
8
-
20
V
V
(BR)G2-SS
gate 2-source breakdown voltage
V
G1-S
= V
DS
= 0; I
G2-S
= 10 mA
8
-
20
V
-
V
(P)G1-S
gate 1-source cut-off voltage
V
G2-S
= 4 V; V
DS
= 8 V; I
D
= 20
A
-
-
2
V
-
V
(P)G2-S
gate 2-source cut-off voltage
V
G1-S
= 4 V; V
DS
= 8 V; I
D
= 20
A
-
-
1.5
V
I
DSS
drain-source current
V
G2-S
= 4 V; V
DS
= 8 V; V
G1-S
= 0
3
15
27
mA
I
G1-SS
gate 1 cut-off current
V
G2-S
= V
DS
= 0; V
G1-S
= 5 V
-
-
50
nA
I
G2-SS
gate 2 cut-off current
V
G1-S
= V
DS
= 0; V
G2-S
= 5 V
-
-
50
nA
SYMBOL
PARAMETER
CONDITIONS
MIN.
TYP.
MAX.
UNIT
y
fs
forward transfer admittance
pulsed; T
j
= 25
C; f = 1 MHz
36
43
50
mS
C
ig1-s
input capacitance at gate 1
f = 1 MHz
2.4
3.1
4
pF
C
ig2-s
input capacitance at gate 2
f = 1 MHz
1.2
1.8
2.5
pF
C
os
output capacitance
f = 1 MHz
1.2
1.7
2.2
pF
C
rs
reverse transfer capacitance
f = 1 MHz
20
30
45
fF
F
noise figure
f = 200 MHz; G
S
= 2 mS; B
S
= B
Sopt
-
0.6
1.2
dB
f = 800 MHz; G
S
= G
Sopt
; B
S
= B
Sopt
-
1.5
2.5
dB
1996 Jul 30
5
Philips Semiconductors
Product specification
Dual-gate MOS-FETs
BF908; BF908R
Fig.4 Transfer characteristics; typical values.
V
DS
= 8 V; T
j
= 25
C.
handbook, halfpage
-
0.6
-
0.4
0
0.2
-
0.2
0.4
VG1-S (V)
3 V
2 V
1.5 V
0.5 V
0 V
0.6
40
30
10
0
20
MRC281
VG2-S = 4 V
1 V
ID
(mA)
Fig.5 Output characteristics; typical values.
V
G2-S
= 4 V; T
j
= 25
C.
handbook, halfpage
0
4
8
16
30
10
0
20
MRC282
12
VDS (V)
ID
(mA)
0.2 V
0.1 V
0 V
-
0.3 V
-
0.2 V
-
0.1 V
VG1-S = 0.3 V
Fig.6
Forward transfer admittance as a function
of drain current; typical values.
V
DS
= 8 V; T
j
= 25
C.
0
10
20
30
40
50
0
5
10
15
20
25
0.5 V
1 V
1.5 V
2 V
3 V
4 V
VG2-S = 0 V
Yfs
(mS)
ID (mA)
MRC280
Fig.7
Forward transfer admittance as a function
of junction temperature; typical values.
0
20
40
60
0
40
80
120
160
40
Yfs
(mS)
T
j
( C)
o
MRC276
V
DS
= 8 V; V
G2-S
= 4 V; I
D
= 15 mA.
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