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參數(shù)資料
| 型號： | P12611EJ1V0AN00 |
| 英文描述： | MCU CMOS 28 LD 20MHZ 8K FLASH, -40C to +85C, 28-SOIC 300mil, TUBE |
| 中文描述： | uPB1509GV 1 GHz的輸入除以2。 4。 8預(yù)分頻器集成電路便攜式無線電系統(tǒng) |
| 文件頁數(shù)： | 15/19頁 |
| 文件大?。?/td> | 110K |
| 代理商： | P12611EJ1V0AN00 |
9
[Pull-Down Resistor on Output Pin to Increase Output Amplitude]
An effective way to increase the output amplitude is to increase the circuit current of the internal output stage by
connecting a DC pull-down resistor to the emitter-follower output pin. The
μ
PB1509GV, however based on the
maximum allowable current of the internal circuits, connect a DC pull-down resistor of 200
MIN to the output pin
(1.2 k
MIN with the
μ
PB587G).
A supplementary explanation follows. In the case of the test circuit shown in the Data Sheet, the specification of
the output amplitude is defined on the load impedance of 200
. Therefore, due to the 1.2 k
pull-down resistor
connection, the circuit current is increased by 2 mA at V
CC
= 3.0 V and output amplitude by about 0.3 V
P-P
, compared
with the above-mentioned test circuit. In addition to this DC effect, the pull-down resistor has the following secondary
effect: although the characteristic impedance of the output pin in the RF range is decreased, this enables to drive a
high-impedance device while maintaining a large amplitude.
Therefore, in actual application sets, you should check first the output amplitude under the load condition of the
application set without connecting the pull-down resistor, then adjust the increase in the circuit current with the pull-
down resistor connected.
3.2 Load Impedance and Characteristics
This IC assures that the output amplitude with a load of 200
is 0.1 V
P-P
MIN. However, this means that Z
L
= 200
at output amplitude measurement is assumed, not that the recommended load impedance is 200
. If a high-
impedance CMOS IC is connected to the following stage, the output amplitude becomes large proportionally to the
load impedance value of the connected IC, and saturates at 1 k
or larger. Figure 3-3 shows the load impedance
dependency of output amplitude for each pull-down resistor value (Rpd), and Figure 3-4 shows the circuit current
dependency of output amplitude (resulting from output pin pull-down resistor) for each load impedance value.
Figure 3-3. Output Amplitude vs. Pull-Down Resistor and Load Impedance
Table 3-1. Relationship between Output Amplitude and Load Impedance
(Underlined values are empirical data for reference only)
Pull-Down Resistor Rpd
Relationship (Approximate Value in Linear Area)
I
CC
Flowing due to Pull-Down Resistor
200
Output saturation area irrespective of Z
L
I
CC
= 14.1 mA
1.2 k
Vout = 0.031
√
Z
L
(V
P-P
) @Z
L
<
360
I
CC
= 7.2 mA
∞
(without Rpd)
Vout = 0.01
√
Z
L
(V
P-P
) @Z
L
<
400
I
CC
= 5.4 mA
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
00
500
1000
1500
Load impedance Z
L
(
)
O
O
(
P
)
2000
2500
1
Rpd = 200
Rpd = 1.2 k
Rpd =
T
A
= +25 C. V
CC
= 3.0 V
f
in
= 408 MHz. P
in
= –20 dBm
Divide ratio ÷ 4
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