Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
ML3371-5P Datasheet(PDF) 11 Page - LANSDALE Semiconductor Inc. |
|
ML3371-5P Datasheet(HTML) 11 Page - LANSDALE Semiconductor Inc. |
11 / 19 page www.lansdale.com Page 11 of 19 Issue A LANSDALE Semiconductor, Inc. ML3371, ML3372 CIRCUIT DESCRIPTION The ML3371 and ML3372 are low power narrowband FM receivers with an operating frequency of up to 60 MHz. Its low voltage design provides low power drain, excellent sensitivity, and good image rejection in narrowband voice and data link applications. This part combines a mixer, an IF (intermediate frequency) limiter with a logarithmic response signal strength indicator, a quadrature detector, an active filter and a squelch trigger cir- cuit. In a typical application, the mixer amplifier converts an RF input signal to a 455 kHz IF signal. Passing through an external bandpass filter, the IF signal is fed into a limiting amplifier and detection circuit where the audio signal is recov- ered. A conventional quadrature detector is used. The absence of an input signal is indicated by the presence of noise above the desired audio frequencies. This “noise band” is monitored by an active filter and a detector. A squelch switch is used to mute the audio when noise or a tone is present. The input signal level is monitored by a meter drive circuit which detects the amount of IF signal in the limiting amplifier. LEGACY APPLICATIONS INFORMATION The oscillator is an internally biased Colpitts type with the collector, base, and emitter connections at Pins 4, 1 and 2 respectively. This oscillator can be run under crystal control. For fundamental mode crystals use crystal characterized paral- lel resonant for 32 pF load. For higher frequencies, use 3rd overtone series mode type crystals. The coil (L2) and resistor RD (R13) are needed to ensure proper and stable operation at the LO frequency (see Figure 13, 45 MHz application circuit). The mixer is doubly balanced to reduce spurious radiation. Conversion gain stated in the AC Electrical Characteristic sta- ble is typically 20 dB. This power gain measurement was made under stable conditions using a 50 Ω source at the input and an external load provided by a 455 kHz ceramic filter at the mixer output which is connected to the VCC (Pin 4) and IF input (Pin 5). The filter impedance closely matches the1.8 kΩ inter- nal load resistance at Pin 3 (mixer output). Since the input impedance at Pin 16 is strongly influenced by a 3.3 kΩ inter- nal biasing resistor and has a low capacitance, the useful gain is actually much higher than shown by the standard power gain measurement. The Smith Chart plot in Figure 17 shows the measured mixer input impedance versus input frequency with the mixer input matched to a 50Ω source impedance at the given frequencies. In order to assure stable operation under matched conditions, it is necessary to provide a shunt resistor to ground. Figures 11, 12 and 13 show the input networks used to derive the mixer input impedance data. Following the mixer, a ceramic bandpass filter is recom- mended for IF filtering (i.e. 455 kHz types having a bandwidth of ±2.0 kHz to ±15 kHz with an input and output impedance from 1.5 kΩ to 2.0 kΩ). The 6 stage limiting IF amplifier has approximately 92 dB of gain. The MC3371 and MC3372 are different in the limiter and quadrature detector circuits. The MC3371 has a 1.8 kΩ and a 51 kΩ resistor providing internal dc biasing and the output of the limiter is internally connected, both directly and through a 10 pF capacitor to the quadrature detector; whereas, in the MC3372 these components are not provided internally. Thus, in the MC3371, no external compo- nents are necessary to match the 455 kHz ceramic filter, while in the MC3372, external 1.8 kΩ and 51 kΩ biasing resistors are needed between Pins 5 and 7, respectively (see Figures 12 and 13). In the MC3371, a parallel LCR quadrature tank circuit is connected externally from Pin 8 to VCC (similar to the MC3361). In the MC3372, a quadrature capacitor is needed externally from Pin 7 to Pin 8 and a parallel LC or a ceramic discriminator with a damping resistor is also needed from Pin 8 to VCC (similar to the MC3357). The above external quadra- ture circuitry provides 90° phase shift at the IF center frequen- cy and enables recovered audio. The damping resistor determines the peak separation of the detector and is somewhat critical. As the resistor is decreased, the separation and the bandwidth is increased but the recovered audio is decreased. Receiver sensitivity is dependent on the value of this resistor and the bandwidth ofthe 455 kHz ceramic filter. On the chip the composite recovered audio, consisting of carrier component and modulating signal, is passed through a low pass filter amplifier to reduce the carrier component and then is fed to Pin 9 which has an output impedance of 450Ω. The signal still requires further filtering to eliminate the carrier component, deemphasis, volume control, and further amplifi- cation before driving a loudspeaker. The relative level of the composite recovered audio signal at Pin 9 should be consid- ered for proper interaction with an audio post amplifier and a given load element. The MC13060 is recommended as a low power audio amplifier. The meter output indicates the strength of the IF level and the output current is proportional to the logarithm of the IF input signal amplitude. A maximum source current of 60 µA is available and can be used to drive a meter and to detect a carri- er presence. This is referred to as a Received Strength Signal Indicator (RSSI). The output at Pin 13 provides a current source. Thus, a resistor to ground yields a voltage proportional to the input carrier signal level. The value of this resistor is estimated by (VCC(Vdc) – 1.0 V)/60 µA; so for VCC = 4.0 Vdc, the resistor is approximately 50 kΩ and provides a maxi- mum voltage swing of about 3.0 V. A simple inverting op amp has an output at Pin 11 and the inverting input at Pin 10. The noninverting input is connected to 2.5 V. The op amp may be used as a noise triggered squelch or as an active noise filter. The bandpass filter is designed with external impedance elements to discriminate between frequen- cies. With an external AM detector, the filtered audio signal is checked for a tone signal or for the presence of noise above the normal audio band. This information is applied to Pin 12. |
Número de pieza similar - ML3371-5P |
|
Descripción similar - ML3371-5P |
|
|
Enlace URL |
Política de Privacidad |
ALLDATASHEET.ES |
¿ALLDATASHEET es útil para Ud.? [ DONATE ] |
Todo acerca de Alldatasheet | Publicidad | Contáctenos | Política de Privacidad | Intercambio de Enlaces | Lista de Fabricantes 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 |