MICRF022BM-FS24 Micrel Inc, MICRF022BM-FS24 Datasheet - Page 9

• Manufacturer Part Number: MICRF022BM-FS24
• Description: IC RECEIVER ASK 300-440MHZ 8SOIC
• Manufacturer: Micrel Inc

Specifications of MICRF022BM-FS24

• Frequency: 300MHz ~ 440MHz
• Sensitivity: -97dBm
• Data Rate - Maximum: 10 kbps
• Modulation Or Protocol: ASK, OOK
• Applications: RKE
• Current - Receiving: 2.2mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 4.75 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -
• Memory Size: -

Step 3: Selecting the C
Extraction of the dc value of the demodulated signal
for purposes of logic-level data slicing is accomplished
using the external threshold capacitor C
chip switched capacitor “resistor” R
block diagram.
Slicing level time constant values vary somewhat with
decoder type, data pattern, and data rate, but typically
values range from 5ms to 50ms. Optimization of the
value of C
Selecting Capacitor C
The first step in the process is selection of a data-slicing-
level time constant. This selection is strongly dependent on
system issues including system decode response time and
data code structure (that is, existence of data preamble,
etc.). This issue is covered in more detail in Application
Note 22.
The effective resistance of R
characteristics table as 145kΩ at 315MHz, this value scales
linearly with frequency. Source impedance of the C
other frequencies is given by Equation 4, where f
MHz:
τ of 5x the bit-rate is recommended. Assuming that a slicing
level time constant τ has been established, capacitor C
may be computed using Equation 5:
A standard ±20% X7R ceramic capacitor is generally
sufficient. Refer to Application Hint 42 for C
selection examples.
Step 4: Selecting the C
The signal path has AGC (automatic gain control) to
increase input dynamic range. The attack time constant of
the AGC is set externally by the value of the C
connected to the C
system range, it is important to keep the AGC control
voltage ripple low, preferably under 10mV
control voltage has attained its quiescent value. For this
reason
recommended.
The AGC control voltage is carefully managed on-chip to
allow duty-cycle operation of the MICRF002. When the
device is placed into shutdown mode (SHUT pin pulled
high), the AGC capacitor floats to retain the voltage. When
operation is resumed, only the voltage droop due to
capacitor leakage must be replenished. A relatively low-
leakage capacitor is recommended when the devices are
used in dutycycled operation.
Micrel, Inc.
July 2008
(4)
(5)
capacitor
TH
is required to maximize range.
R
C
SC
TH
AGC
values
=
=
TH
145kΩ
R
pin of the device. To maximize
TH
AGC
τ
SC
Capacitor
Capacitor
of
SC
4.8970
is listed in the electrical
f
at
T
least
SC
, shown in the
TH
TH
PP
AGC
0.47µF
and the on-
and CAGC
once the
capacitor
TH
T
pin at
is in
are
TH
9
To further enhance duty-cycled operation, the AGC push
and pull currents are boosted for approximately 10ms
immediately after the device is taken out of shutdown. This
compensates for AGC capacitor voltage droop and reduces
the time to restore the correct AGC voltage. The current is
boosted by a factor of 45.
Selecting C
A C
recommended. The value of the C
minimize the ripple on the AGC control voltage by using a
sufficiently large capacitor. However if the capacitor is too
large the AGC may react too slowly to incoming signals.
AGC settling time from a completely discharged (zero-volt)
state is given approximately by Equation 6:
where:
Selecting C
Voltage droop across the C
should be replenished as quickly as possible after the IC is
enabled. As mentioned above, the MICRF002 boosts the
push-pull current by a factor of 45 immediately after start-
up. This fixed time period is based on the reference
oscillator frequency f
and varies inversely with f
and the duration of the shutdown time period should be
selected such that the droop can be replenished within this
10ms period.
Polarity of the droop is unknown, meaning the AGC voltage
could droop up or down. Worst-case from a recovery
standpoint is downward droop, since the AGC pull-up
current is 1/10th magnitude of the pulldown current. The
downward droop is replenished according to the Equation
7:
where:
For example, if user desires ∆t = 10ms and chooses a
4.7µF C
Using the same equation with 200nA worst case pin
leakage and assuming 1µA of capacitor leakage in the
same direction, the maximum allowable ∆t (shutdown time)
is about 0.56s for droop recovery in 10ms.
The ratio of decay-to-attack time-constant is fixed at 10:1
(that is, the attack time constant is 1/10th of the decay time
constant). Generally the design value of 10:1 is adequate
AGC
capacitor in the range of 0.47µF to 4.7µF is typically
(6)
C
(7)
I = AGC pullup current for the initial 10ms (67.5µA)
C
∆t = droop recovery time
∆V = droop voltage
AGC
AGC
AGC
, then the allowable droop is about 144mV.
AGC
AGC
sin in µF, and ∆t is in seconds.
= AGC capacitor value
Capacitor in Continuous Mode
Capacitor in Duty-Cycle Mode
∆t
C
AGC
I
=
T
. The time is 10.9ms for f
1.333C
=
∆V
∆t
T
AGC
. The value of C
AGC
capacitor during shutdown
AGC
−
0.44
should be selected to
MICRF002/RF022
M9999-070808
AGC
T
= 6.00MHz,
capacitor