MICRF033BM Micrel Inc, MICRF033BM Datasheet - Page 9

• Manufacturer Part Number: MICRF033BM
• Manufacturer: Micrel Inc

Specifications of MICRF033BM

• Lead Free Status / Rohs Status: Not Compliant

October 1999
MICRF003
The signal path has automatic gain control (AGC) to
increase input dynamic range.
CAGC, must be connected to the CAGC pin of the device.
The ratio of decay-to-attack time-constant is fixed at 10:1
(i.e., the attack time constant is 1/10th the decay time
constant), and this ratio cannot be changed by the user.
However, the attack time constant is selectable by the user
through the value of capacitor CAGC.
[By adding resistance from the CAGC pin to VDDBB or
VSSBB in parallel with the CAGC capacitor, the ratio of
decay-to-attack time-constant may be varied, although the
value of such adjustments must be studied on a per-
application basis.
adequate for the vast majority of applications.]
“Application Note TBD”.
To maximize system range, it is important to keep the AGC
control voltage ripple low, preferably under 10mVpp once
the control voltage has attained its quiescent value. For this
reason capacitor values
The AGC control voltage is carefully managed on-chip to
allow duty-cycle operation of the MICRF003 in excess of
100:1. When the device is placed into SHUT mode (i.e.,
SHUT pin pulled high), the AGC capacitor is “floated”, to
retain the voltage. When operation is resumed, only the
voltage droop on the capacitor associated with leakage
must be replenished.
capacitor is recommended for duty cycle operation. The
actual tolerable leakage will be application dependent.
Clearly, leakage performance is less critical when the
device off-time is low (milliseconds), and more critical when
the off-time is high (seconds).
To further enhance Duty-cycle operation of the IC, the AGC
push and pull currents are increased for a fixed time
immediately after the device is taken out of Shutdown mode
(i.e., turned-on).
voltage “droop” while the IC is in Shutdown, reduces the
time to reacquire the correct AGC voltage, and thus extends
maximum achievable duty ratios. Push/Pull currents are
increased by 45X their nominal values.
period is based on the REFOSC frequency Ft, 9.7msec for
Ft = 6.75MHz, and varies inversely as Ft varies, by the
scale factor Ft / 6.75, where Ft is in MHz.
Reference Oscillator (REFOSC) and External Timing
Element
All timing and tuning operations on the MICRF003 are
derived from the REFOSC function.
single-pin Colpitts-type oscillator. The user may handle this
pin in one of three possible ways:
The third approach is attractive for further lowering system
cost if an accurate reference signal exists elsewhere in the
(1) connect a ceramic resonator, or
(2) connect a crystal, or
(3) drive this pin with an external timing signal.
This compensates for AGC capacitor
Generally the design value of 10:1 is
0.47uF are recommended.
Thus a relatively low-leakage
An external capacitor,
This function is a
The fixed time
QwikRadio
See
9
system (e.g., a reference clock from a crystal or ceramic
resonator-based microprocessor).
signal should be AC-coupled, and resistively-divided down
(or otherwise limited) to approximately 0.5Vpp. The specific
reference frequency required is related to the system
transmit frequency, and to the operating mode of the device
as set by the SWEN control pin.
TBD” for a discussion of frequency selection and accuracy
requirements.
Wakeup Function
The Wakeup function is made available for the purposes of
further reducing power consumption of the overall wireless
system.
active when the IC detects a constant RF Carrier “header” in
the demodulated output signal.
active-low.
external circuits, like a data decoder or microprocessor,
only at times when there is a reasonable expectation of an
incoming RF signal. The Wakeup function is unavailable
when the IC is in SHUT mode.
The Wakeup function is composed of a resettable counter,
based on an internal 27.5kHz clock (based on a 7.04Mhz
reference frequency). To utilize this function, a burst of RF
Carrier in excess of 5msec must be placed at the start of
each data code word, or a single 5msec RF carrier tone at
the start of the data pattern (clearly the former is preferred
to improve communication reliability). When this constant
carrier tone is detected, without interruption, for 128 clock
cycles of 27.5kHz, WAKEB will transition low, and stay low
until data begins. This particular approach is utilized over
others (1) since constant tones in excess of 5msec are very
rare, leading to few false-positive indications, and (2) this
technique does not require the introduction of a signal path
offset, which impacts achievable range.
[Note: For designers who wish to use the Wakeup function
while “squelching” the output, a positive squelching offset
voltage must be used. This simply requires the squelch
resistor be taken to a voltage more positive than the
quiescent voltage on pin CTH, so that the data output is low
in absence of a transmission.]
Shutdown Function
The Shutdown function is controlled by the logic state of
SHUT. When SHUT is high, the device goes into low-power
standby mode, consuming less than 1 A. This pin is pulled
high internally, and so must be pulled low to engage the
device.
MICRF003 Frequency and Capacitor Selection
Selection of the REFOSC frequency Ft, Slicing Level (CTH)
capacitor, and AGC capacitor are briefly summarized in this
section.
details.
tm
Please see Application Note TBD for complete
WAKEB is an output logic signal, which goes
This output may be used to “wakeup” other
Sense of the signal is
An externally applied
See “Application Note
MICRF003
Micrel