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ML13156 Datasheet(PDF) 6 Page - LANSDALE Semiconductor Inc. |
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ML13156 Datasheet(HTML) 6 Page - LANSDALE Semiconductor Inc. |
6 / 21 page ML13156 LANSDALE Semiconductor, Inc. GENERAL The ML13156 is a low power single conversion wideband FM receiver incorporating a split IF. This device can be used as a single conversion receiver or as the backend in digital FM systems such as CT–2 and wide band data links with data rates up to 500 kbaud. It contains a mixer, oscillator, signal strength meter drive, IF amplifi- er, limiting IF, quadrature detector and a data slicer with a hold function (refer to Figure 8, Simplified Internal Circuit Schematic). CURRENT REGULATION Temperature compensating voltage independent current regula- tors are used throughout. MIXER The mixer is a double–balanced four quadrant multiplier and is designed to work up to 500 MHz. It can be used in differential or in single–ended mode by connecting the other input to the positive supply rail. Figure 4 shows the mixer gain and saturated output response as a function of input signal drive. The circuit used to measure this is shown in Figure 1. The linear gain of the mixer is approxi- mately 22 dB. Figure 9 shows the mixer gain versus the IF out- put frequency with the local oscillator of 150 MHz at 100 mVms LO drive level. The RF frequency is swept. The sensitivi- ty of the IF output of the mixer is shown in Figure 10 for an RF input drive of 10 mVrms at 140 MHz and IF at 10 MHz. The single–ended parallel equivalent input impedance of the mixer is Rp ~ 1.0 k Ω and Cp ~ 4.0 pF (see Table 1 for details). The buffered output of the mixer is internally loaded resulting in an output impedance of 330 Ω. LOCAL OSCILLATOR The on–chip transistor operates with crystal and LC resonant elements up to 220 MHz. Series resonant, overtone crystals are used to achieve excellent local oscillator stability. 3rd overtone crystals are used through about 65 to 70 MHz. Operation from 70 MHz up to 180 MHz is feasible using the on–chip transistor with a 5th or 7th overtone crystal. To enhance operation using an overtone crystal, the internal transistor’s bias is increased by adding an external resistor from Pin 23 to VEE. –10 dBm of local oscillator drive is needed to adequately drive the mixer (Figure 10). The oscillator configurations specified above, and two others using an external transistor, are described in the application sec- tion: 1) A 133 MHz oscillator multiplier using a 3rd overtone crystal, and 2) A 307.8 to 309.3 MHz manually tuned, varactor controlled local oscillator. RSSI The Received Signal Strength Indicator (RSSI) output is a cur- rent proportional to the log of the received signal amplitude. The RSSI current output is derived by summing the currents for the IF and limiting amplifier stages. An external resistor at Pin 20 sets the voltage range or swing of the RSSI output voltage. Linearity of the RSSI is optimized by using external ceramic or crystal bandpass filters which have and insertion loss of 8.0 dB. The RSSI circuit is designed to provide 70+ dB of dynamic range with temperature compensation (see Figures 6 and 7 which show RSSI responses of the IF and Limiter amplifiers). Variation in the RSSI output current with supply voltage is 5 ma total delta (see Figure 11). CARRIER DETECT When the meter current flowing through the meter load resist- ance reaches 1.2 Vdc above ground, the comparator flips, caus- ing the carrier detect output to go high. Hysteresis can be accomplished by adding a very large resistor for positive feed- back between the output and the input of the comparator. IF AMPLIFIER The first IF amplifier section is composed of three differential stages with the second and third stages contributing to the RSSI. This section has internal dc feedback and external input decou- pling for improved symmetry and stability. The total gain of the IF amplifier block is approximately 39 dB at 10.7 MHz. Figure 5 shows the gain and saturated output response of the IF ampli- fier over temperature, while Figure 12 shows the IF amplifier gain as a function of the IF frequency. The fixed internal input impedance is 1.4k Ω. It is designed for application where a 455 kHz ceramic filter is used and no exter- nal output matching is necessary since the filter requires a 1.4 k Ω source and load impedance. For 10.7 Mhz ceramic filter applications, an external 430 Ω resistor must be added in parallel to provide the equivalent load impedance of 330 Ω that is required by the filter; however, no external matching is necessary at the input since the mixer out- put matches the 330 Ω source impedance of the filter. For 455 kHz applications, an external 1.1 k Ω resistor must be added in series with the mixer output to obtain the required matching impedance of 1.4 k Ω of the filter input resistance. Overall RSSI linearity is dependent on having total midband attenuation of 12 dB (6.0 dB insertion loss plus 6.0 dB impedance matching loss) for the filter. The output of the IF amplifier is buffered and the impedance is 290 Ω. LIMITER The limiter section is similar to the IF amplifier section except that four stages are used with the last three contributing to the RSSI. The fixed internal input impedance is 1.4 k Ω. The total gain of the limiting amplifier sections is approximately 55 dB. This IF limiting amplifier section internally drives the quadra- ture detector section. CIRCUIT DESCRIPTION www.lansdale.com Page 6 of 21 Issue A |
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