IC-7300 MAIN UNIT

| abril 5, 2016

IC-7300

CIRCUIT DESCRIPTION MAIN UNIT

The IC-7300 uses the Direct Conversion system, which directly converts the received signal into a digital signal by the A/D converter. The digital signal is then converted into the 36 kHz IF signal by the FPGA, before being processed by the DSP.

The transmit signal is processed and converted into the transmit IF signal by the DSP. The transmit IF signal is converted into an RF signal by the FPGA, and then converted into an analog transmit signal. Since the IF signal is directly processed as a digital signal in the FPGA, any analog heterodyne circuits, such as IF circuits, are not needed.

IC-7300 inside view Main Unit

1. RECEIVE SIGNAL PROCESSING

• External attenuator and A/D conversion

The received signal from the RF UNIT is passed through the TX/RX switching diode (D1231) and applied to the external attenuator (PIN diode D1251). The attenuator is controlled by the AGC voltage from the D/A converter (IC971PCM1754DBQR) to adjust the received signal level so that the signal amplitude is within the input dynamic range of the A/D converter.

In a traditional transceiver, the received signal level (gain) was controlled by the DSP prior to the external AGC circuit.

But, this method will not work in the Direct Sampling system since the RF gain control cannot prevent over input to the A/D converter. This method has been replaced by adding an external AGC circuit, instead of using the DSP’s internal AGC circuitry.

The level-adjusted received signal is applied to the A/D converter to be converted into a digital signal. The converted digital signal is applied to the FPGA (IC1351 – EP4CE55F23I7N) where the received signal is converted into the 36 kHz IF signal.

• FPGA

FPGA (Field-Programmable Gate Array) is a device that can digitally configure the virtual circuit in the chip.

IC-7300 FPGA Block DiagramIC-7300 FPGA Block Diagram

The program that determines how it operates is written in the external EEPROM, and loaded when the transceiver power is turned ON. So the circuit can be reconfigured, even after the device is mounted on the PCB, by reprogramming it.

Using mathematical functions, the FPGA (IC1351) performs down conversion and filtering by controlling digital bits.

The received signal from the RF UNIT has been converted into a digital data stream by the A/D converter. The converted data is applied to the FPGA as a bit stream with the sampled signal spectrum, and then processed by manipulating the digital bits. The FPGA processes the signal mathematically to digitally obtain the oscillation and mixing (Image rejection mixer), as if the signal is processed in a hardware down conversion circuit.

The processed signal is applied to the DSP (IC901 – TMS320C6745DPTPA3).


• Demodulator and D/A converter

The 36 kHz IF signal is digitally demodulated and processed by the DSP (IC901), whose design is based totally on that of the IC-7100. The internal AGC control, demodulation, noise reduction (NB, NR and Notch filter) and squelch functions are also the same as those of the IC-7100.

The demodulated and processed signal from the DSP (IC901) is applied to the D/A converter (IC991 – PCM1754DBQR) to be converted into an analog AF signal. The AF signal is then applied to the AF circuit.

• AF circuit

The AF signal is amplified by the AF AMP (IC992 – TS462CPT), and then by the D-class AF power AMP (IC721 – MP7741DQ-LF-P) to obtain up to 2.5 watts (at 8 ohms, 1 kHz, 10% distortion) of output power. The amplified signal is applied to the speaker through the LPF (L731, L732 and C731 ~ C735), which attenuates unwanted frequency components, and to the speaker SW (Q746).

When an external speaker is connected to the [EXT-SP] jack, the audio output from the internal speaker (SP1) is disconnected.

2. TRANSMIT SIGNAL PROCESSING

• MIC AMP and A/D converter

The audio signal from the [MIC] connector on the front panel is amplified by the MIC amplifier (IC1002 – TS462CPT), and then applied to the A/D converter (IC1001 – PCM1802DBR) to be converted into a digital signal. The audio signal from the [ACC] socket is applied to the A/D converter (IC1001), through the mute SW (IC1003 – TC7W53FK (TE85LF) and LPF (IC1002), and is also converted into a digital signal. The converted digital signal is then applied to the DSP (IC901 – TMS320C6745DPTPA3) for audio processing.

• Modulation and D/A converter

The signal is digitally modulated in the DSP (IC901), resulting in the 36 kHz transmit IF signal, and then applied to the FPGA (IC1351).

The audio signal from the microphone has been converted into a digital data stream by the A/D converter. The converted data is applied to the DSP (IC901), and digitally processed, resulting in a modulated 36 kHz transmit IF signal.

• FPGA

The transmit IF signal is applied to the FPGA (IC1351). The FPGA mathematically processes the signal to digitally obtain the oscillation (TX LO) and mixing (Image rejection mixer), as if the signal is processed in a hardware up conversion circuit.

The processed signal is applied to the D/A converter to be converted in to an analog RF transmit signal.

• RF signal processing

The transmit signal, that is processed and up-converted in the FPGA (IC1351 – EP4CE55F23I7N), is applied to the D/A converter (IC1331 – ISL5857IAZ) to be converted into an analog transmit signal. The transmit signal is passed through the LPF (L1281, L1282, C1281, C1283 and C1285), which attenuates unwanted frequency components in the transmit signal, and is then applied to the RF UNIT.

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