IC-756Pro2_circuit_description.pdf

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1、CIRCUIT DESCRIPTION 1 1 RECEIVER CIRCUITS 1-1 RF SWITCHING CIRCUIT (CTRL AND RF-A UNITS) The RF switching circuit leads receive signals to bandpass filters from an antenna connector while receiving. However, the circuit leads the signal from the RF power amplifier to the antenna connector while tran

2、smitting. RF signals from ANT 1 or ANT 2 pass through the anten- na selector (RL3), transmit/receive switching relays (RL1, RL2, RL4), and low-pass filter (L27, L28, C63C66, C105), and are then applied to the RF-A unit via J2. The signals from the CTRL unit either bypass or pass through the 6 dB (RF

3、-A unit, RL121, R121) and/or 12 dB (RF-A unit, RL122, R123) attenuators via the antenna selec- tor (RL101). By selecting the attenuators, 0 (bypass), 6, 12 and 18 dB attenuations are obtained. The signals are then applied to the RF filters. When the RX ANT is selected, the RF signals are passed thro

4、ugh the low-pass filter (RF-A unit, L112, L111, C111C116), then applied to the antenna selector (RF-A unit, RL101). 1-2 RF BANDPASS FILTER CIRCUIT (RF-A UNIT AND BPF BOARD) RF bandpass filters pass only the desired band signals and suppress any undesired band signals. The RF circuit has 11 bandpass

5、filters and 1 low-pass filter. (1) 0.031.6 MHz (BPF BOARD) The signals pass through the low-pass filter (L181L183, C181C185), attenuator (R181R183), and are then applied to the RF amplifiers (Q501, Q601). (2) 1.660 MHz (RF-A UNIT AND BPF BOARD) The signals pass through the high-pass filter (L171L174

6、, C171C174) to suppress excessively strong signals below 1.6 MHz. The filtered signals are applied to one of 11 band- pass filters on the table at right above, and then applied to or bypassed the pre-amplifier circuit. 1-3 PRE-AMPLIFIER CIRCUITS (RF-A UNIT) The IC-756PROhas 2 gain levels of pre-ampl

7、ifier circuits. One has 10 dB gain for the 1.821 MHz bands and the other one has 16 dB gain for the upper 24 MHz bands. When the P.AMP switch is set to P.AMP1 or P.AMP2, the signals are applied to the pre-amplifier 1 (Q441, Q442) or pre-amplifier 2 (IC451) circuit, respectively. Pre-amplified or byp

8、assed signals are applied to the RF amplifier circuits (Q501, Q502 and Q601, Q602). 1-4 RF AMPLIFIER AND 1ST MIXER CIRCUITS (RF-A UNIT) The 1st mixer circuit mixes the receive signals with the 1st LO signal to convert the receive signal frequencies into a 64.455 MHz 1st IF signal. The IC-756PROhas t

9、wo 1st mixer circuits for the dualwatch function. The signals from the pre-amplifier circuit, or signals which bypass the pre-amplifiers, are divided at L491. Each signal is applied to a 60 MHz cut-off low-pass filter, RF amplifier (Q501, Q502 and Q601, Q602) and then to a 1st mixer (Q511Q514 or Q61

10、1Q614). Each 1st LO signal (64.4850124.4550 MHz) enters the RF -A unit from the PLL unit via J561 or J661. The LO signals are amplified at the LO amplifier (Q561 or Q661), filtered by a low-pass filter, and then applied to each 1st mixer. Used RF filter * : On the BPF board Receiver construction LPF

11、 or BPF 1st LO B 1st LO A 2nd LO 64.0 MHz Crystal filter FI711a/b 1st mixer A Q511Q514 1st mixer B Q611Q614 2nd mixer Q941Q944 3rd LO 491 kHz 3rd mixer IC151 64.455 MHz 0.0360.0 MHz Ceramic filter FI132, FI111 455 kHz to squelch gate (IC301) 36 kHzDSP-A board RF-A UNITMAIN-A UNIT Band 0.031.6 MHz 1.

12、62 MHz 23 MHz 34 MHz 46 MHz 68 MHz 811 MHz Band 1115 MHz 1522 MHz 2230 MHz 3050 MHz 5054 MHz 5460 MHz Control signal B7 B8 B9 B10W B10 B10W Control signal B0 B1 B2 B3 B4 B5 B6 Input diode N/A *D2001 *D2021 *D2041 *D2061 *D2081 D261 Input diode D281 D301 D321 D341 D361 D341 Downloaded by? RadioAmateu

13、r.EU 2 1-5 1ST IF CIRCUIT (RF-A UNIT) The 1st IF circuit filters and amplifies the 1st IF signal. The 1st IF signal combined at L653 is applied to a pair of MCF (Monolithic Crystal Filter; FI711a/b) to suppress out-of-band signals. The level of converted 1st IF signal is adjusted at the PIN attenuat

14、ors (D531D533, D535 or D631D633, D635) con- trolled by the BAL controller for the dualwatch function. The signal is applied to the 1st IF amplifier (Q551 or Q651) and then combined at L653. The combined signal passes through the 3 dB attenuator (R711R713) and MCFs (FI711a/b). The signal is amplified

15、 at the 1st IF amplifier (Q721). The amplified signal is then applied to the 2nd mixer circuit. 1-6 2ND MIXER CIRCUIT (RF-A UNIT) The 2nd mixer circuit mixes the amplified 1st IF signal and 2nd LO signal (64.00 MHz) for conversion into the 2nd IF signal. The 1st IF signal from the 1st IF amplifier (

16、Q721) is convert- ed into a 455 kHz 2nd IF signal at the 2nd mixer circuit (D941). The 2nd IF signal is applied to the noise blanker gate (MAIN- A unit) via the J741. 1-7 NOISE BLANKER CIRCUIT (MAIN-A UNIT) The noise blanker circuit detects pulse-type noise, and turns OFF the signal line when the no

17、ise appears. The 2nd IF signal from the RF-A unit is applied to the noise blanker gate (D112, D116). A portion of the 2nd IF signal from RF-A unit is amplified at the noise amplifiers (Q271Q273, Q279), and is then detected at the noise detector (D271) to convert the noise components to DC volt- ages

18、. The signal is then applied to the noise blanker switch (Q276, Q278). At the moment the detected voltage exceeds Q276s threshold level, Q278 outputs a blanking signal to close the noise blanker gate (D113, D114). The PLL unlock signal are also applied to Q278, to control the noise blanker gate. Som

19、e DC voltage from the noise detector circuit is fed back to the noise amplifiers (Q271Q273) via the DC amplifiers (Q274, Q275). The DC amplifiers function as an AGC circuit to reduce average noise. Therefore, the noise blanker func- tion shuts off pulse-type noise only. 1-8 2ND IF CIRCUIT (MAIN-A UN

20、IT) The 2nd IF circuit amplifies and filters the 2nd IF signal, and applies the 2nd IF signal to the 3rd mixer circuit. The 2nd IF signal from the noise blanker gate (D113, D114) is amplified at the 2nd IF amplifier (Q141) and passed through the ceramic filter (FI111). The filtered signal is applied

21、 to the 3rd mixer circuit. 1-9 3RD MIXER AND 3RD IF CIRCUITS (MAIN-A UNIT) The 3rd mixer circuit mixes the 2nd IF signal and the 3rd LO signal to obtain the 3rd IF (36 kHz) signal. The 2nd IF signal from the ceramic filter (FI111) is applied to the 3rd mixer circuit (IC151, pin 1). The 3rd LO signal

22、 from the PLL unit is applied to the 3rd mixer (IC151, pin 5). The mixed signal is output from pin 6. The 3rd IF signal is passed through the low-pass filter (IC201a) and amplified at the 3rd IF amplifier (IC201b). The filtered and amplified signal is then applied to the DSP-A board via DRIF line. 1

23、-10 DSP RECEIVER CIRCUIT (DSP-A BOARD) The DSP (Digital Signal Processor) circuit enables digital IF filter, digital noise reduction, digital PSN (Phase Shift Network)/Low Power/Phase demodulation, digital automatic notch, and etc. The 36 kHz 3rd IF signal from the 3rd IF amplifier (MAIN-A unit, IC2

24、01b) is amplified at the differential amplifiers (IC2301a/b) after being passed through the T/R switch (IC2291), and is then applied to the A/D converter (IC2321). The coverted signal is level shifted 5V to 3.3 V at the level converter (IC2051). Differential converter A/D converter DRIF DRAF DSP rec

25、eiver circuit 6 7 1 IC2291 IC2301b/aIC2321 Level converter IC2051 D/A converter IC2052 Level converter IC2351 DSP IC IC2001 LPF IC2401 T/R switch 13 12 14 IC2372x 15 9 1 IC2372y HPF IC2441a Mixer amplifier IC2381b 5 3 4 IC2372z 7 4 1 IC2473 MAIN-A unitDSP-A boardMAIN-A unit 36 kHz 3rd IF signal AF s

26、ignals “TXS” signal “TXS” signal “TXS” signal 5 11 10 3 The level shifted signal is applied to the DSP IC (IC2001) for 36 kHz digital IF filter, demodulation, automatic notch and noise reduction, etc. The output signal is level shifted 3.3 V to 5V at the level converter (IC2052), and is applied to t

27、he D/A converter (IC2351) to convert into the analog audio sig- nals. The converted audio signals are passed through the active filter (IC2371a), AF amplifier (IC2371b), analog switches (IC2372, pins 14, 13 and pins 1, 15) then applied to the low- pass filter (IC2401). The filtered signals are passe

28、d through the analog switches (IC2372, pins 4, 3 and IC2473, pins 1, 7), high-pass filter (IC2441A) and mixer amplifier (IC2471A), and then applied to the MAIN-A unit via J2001 (pin 13) as the DRAF signal. 1-11 TWIN PBT CIRCUIT (DSP-A BOARD) General PBT (Passband Tuning) circuit shifts the center fr

29、e- quency of IF signal to electronically narrow the passband width. The IC-756PROuses the DSP circuit for the digital PBT function and actually shifts the both lower and higher passbands of 3rd IF filter within 1.8 kHz. The twin PBT circuit in DSP IC (IC2001) controlled by the TWIN PBT controller ad

30、justs the 3rd IF passband width and rejects interference. 1-12 AGC CIRCUIT (DSP-A BOARD) The AGC (Automatic Gain Control) circuit reduces IF ampli- fier gain and attenuates IF signal to keep the audio output at a constant level. The receiver gain is determined by the voltage on the AGC line (IC2461,

31、 pin 4). The D/A converter for AGC (IC2461) supplies control voltage to the AGC line and sets the receiv- er gain with the RF/SQL control. The 3rd IF signal from the level converter (IC2051) is detect- ed at the AGC detector section in DSP IC (IC2001), and is applied to the D/A converter for AGC via

32、 the level converter (IC2052). The AGC voltage is amplified at the buffer amplifi- er (IC2471b) and is applied to the MAIN-A unit to control the AGC line. When receiving strong signals, the detected voltage increas- es and the AGC voltage decreases via the buffer amplifier (IC2471b). As the AGC volt

33、age is used for the bias voltage of the IF amplifier (RF-A unit; Q721), IF amplifier gain is decreased. 1-13 S-METER CIRCUIT (MAIN-A UNIT) The S-meter circuit indicates the relative received signal strength while receiving by utilizing the AGC voltage which changes depending on the received signal s

34、trength. A portion of the AGC bias voltage from the DSP-A board is applied to the differential amplifier (IC101a, pin 2) where the difference between the AGC and reference voltage is detect- ed. The detected voltage is passed through the analog switch (IC3631, pins 12, 14) as the SML signal and appl

35、ied to the main CPU (IC3501, pin 108) to activate the S/RF meter via the sub CPU (IC401) on the DISPLAY board. 1-14 SQUELCH CIRCUIT (MAIN-A UNIT) The squelch circuit mutes audio output when the S-meter signal is lower than the RF/SQL setting level. The S-meter signal is applied to the main CPU (IC35

36、01, pin 108) and is compared with the threshold level set by the RF/SQL control. The RF/SQL setting signal is applied to the main CPU via the sub CPU (DISPLAY board; IC401, pin 91). The main CPU analyzes the compared signal and out- puts control signal to the squelch gate (IC301, pin 5) via the inte

37、rface IC (IC3653, pin 19) to open or close the squelch as the SQLS signal. 1-15 AF AMPLIFIER CIRCUIT (MAIN-A UNIT) The AF amplifier amplifies the audio signals to a suitable dri- ving level for the speaker. The AF signals (DRAF) from the DSP-A board are passed through the squelch gate (IC301) and am

38、plified at the AF amplifier section of IC311 (pins 2, 4), and volume is con- trolled by the AFGV signal at the VCA section (pins 79). The volume controlled AF signals are passed through the AF mute gate (IC331, pins 1, 7), then applied to the AF power amplifier (IC332, pin 1) via the ripple filter (

39、Q331). The amplified audio signals are passed through the PHONES and EXT SP jacks then applied to the internal speaker when no plug is connected to the jacks. The AF mute gate is controlled by the AF control via the sub and main CPUs. PHONES EXT SP Int. speaker IC332 AF power amp. DRAF AF amplifier

40、circuit 7 6 1 IC301IC311 Mute switchSquelch gate Ripple filter Q331 MAIN-A unitDSP-A board “SQLS” signal “AFGV” signal 5 6 7 1 IC331 “AFMS” signal 2 AMPVCA 4 2 TRANSMITTER CIRCUITS 2-1 MICROPHONE AMPLIFIER CIRCUIT (MAIN-A UNIT) The microphone amplifier circuit amplifies microphone audio signals to a

41、 level needed for the DSP circuit. Audio signals from the MIC connector (MIC board; J1, pin 1) are amplified at the audio amplifier section in IC451 (pins 21, 22) via the analog switch (IC3002, pins 12, 14), then applied to the buffer amplifier section (IC451, pin 5) and VCA section. The gain contro

42、lled signals are output from (IC451, pin 9) and passed through the analog switch (IC3005, pins 14, 12) and then applied to the DSP circuit as the DTAF signal. The VCA section in IC451 (pins 79) controls microphone input gain according to the MIC GAIN control level using the MIGV signal coming from t

43、he main CPU via the I/O expander (IC3751, pin 4). 2-2 VOX CIRCUIT (MAIN-A UNIT) The VOX (Voice-Operated Transmission) circuit sets trans- mitting conditions according to voice input. A portion of the amplified audio signals from the AF amplifi- er section in IC451 are again amplified at the VOX ampl

44、ifier section IC451 (pin 9), also gain contolloed signals at the VCA section (pin 9) are amplified at the AF amplifier (IC3004b, pins 6, 7), and then applied to the main CPU (IC3501, pin 106) after passing through the analog switch (IC362, pins 6, 1) as the VOXL signal. The VOGV signal is applied to

45、 the VCA section in IC3003 (pin 79) from the main CPU via the I/O expander (IC3751, pin 9) to adjust VOX actionable sensitivity. This is controlled by the VOX gain set in the VOX SET mode. 2-3 DSP TRANSMITTER CIRCUIT (DSP-A BOARD) The microphone audio signals from the MAIN-A unit via the DTAF line a

46、re applied to the analog switch (IC2201, pin 4) and output from pin 3 or 5 to the each modulation circuits. (1) When SSB mode The audio signals from the analog switch (IC2201, pin 5) are amplified at the limitter amplifier (IC2281b) and applied to the low-pass filter (IC2281d/c) to limit the transmi

47、t passband width. The filtered signals are then applied to the differential ampli- fiers (IC2301a/b) via the analog switch (IC2201) and T/R switch (IC2291). (2) When FM/AM modes The audio signals from the analog switch (IC2201, pin 3) are applied to the modulation adjustment pots (R2227: FM mode, R2

48、229: AM mode) via the limitter amplifier, pre- emphasis circuit (only FM mode) and splatter filter consist of IC2211. The level adjusted signals are applied to the differ- ential amplifiers (IC2301a/b) after being passed through the analog switch (IC2201) and T/R switch (IC2291). The pre- emphasis c

49、ircuit is cancelled by Q2201, Q2202, Q2211 on AM mode. The amplified signals at the differential amplifiers (IC2301a/b) are applied to the A/D converter (IC2321). The coverted signals are level shifted 5V to 3.3 V at the level converter (IC2051). The level shifted signal is applied to the DSP IC (IC2001) and modulated at the DSP IC to produce the 36 kHz trans- mitter IF signal. The modulated IF signal from the DSP IC is level shifted 3.3 V to 5V at the level converter (IC2052), and is applied to the D/A converter (IC2351) to convert into the analog IF signal. The converted IF signal is