 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
MICRF003 Datasheet(PDF) 9 Page - Micrel Semiconductor |
|
||||||||||||||||||||||||||||||
MICRF003 Datasheet(HTML) 9 Page - Micrel Semiconductor |
|
|
9 / 16 page  QwikRadio tm 9 October 1999 MICRF003 MICRF003 Micrel The signal path has automatic gain control (AGC) to increase input dynamic range. An external capacitor, 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. Generally the design value of 10:1 is adequate for the vast majority of applications.] See “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 ≥ 0.47uF are recommended. 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. Thus a relatively low-leakage 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). This compensates for AGC capacitor 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. The fixed time 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. This function is a single-pin Colpitts-type oscillator. The user may handle this pin in one of three possible ways: (1) connect a ceramic resonator, or (2) connect a crystal, or (3) drive this pin with an external timing signal. The third approach is attractive for further lowering system cost if an accurate reference signal exists elsewhere in the system (e.g., a reference clock from a crystal or ceramic resonator-based microprocessor). An externally applied 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. See “Application Note 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. WAKEB is an output logic signal, which goes active when the IC detects a constant RF Carrier “header” in the demodulated output signal. Sense of the signal is active-low. This output may be used to “wakeup” other 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 µA. 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. Please see Application Note TBD for complete details. |
Similar Part No. - MICRF003 |
|
Similar Description - MICRF003 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
