Icom IC-F7000 DSP Receiver Circuit Main and DSP Units, AGC Circuit DSP and Main Units

4-1-5 DSP RECEIVER CIRCUIT (MAIN AND DSP UNITS)

The DSP (Digital Signal Processor) circuit enables digital IF filter, digital noise reduction, digital PSN (Pulse Shift Network), phase demodulation, digital automatic notch, and etc.

The 3rd IF signal is applied to the IF amplifier (MAIN unit; IC1002, pin 5) after being passed through the low-pass filter (MAIN unit; IC1002, pins 3, 1). The amplified 12 kHz 3rd IF signal is amplified at the differential amplifiers (IC9651a/b), and is then applied to the A/D convertor section in the CODEC IC (IC9501) on the DSP board. At the same time, the converted signal is level-shifted 5 V to 3.3 V in the IC (IC9501).

The level-shifted signal is applied to the DSP IC (IC9301) for the digital IF filter, demodulator, automatic notch and noise reduction, etc.

The output signal from the DSP IC is applied to the D/A con- verter section in the CODEC IC (IC9501) to convert into the analog audio signals. Also the signals are level-shifted 3.3 V to 5 V at the level converter section in the IC (IC9501).

The level-shifted audio signals are passed through the active filter (IC9701a), and then applied to the MAIN unit via J9901 (pin 22) as the “DSP02” signal.

4-1-6 AGC CIRCUIT (DSP AND MAIN UNITS)

The AGC (Automatic Gain Control) circuit reduces IF ampli- fier gain and attenuates IF signal to keep the audio output at a constant level.

• DSP CIRCUIT

The receiver gain is determined by the voltage on the AGC1 line from the DSP unit. The D/A converter for the AGC (IC9102) supplies control voltage to the AGC1 line and sets the receiver gain with the [RF/SQL] control.

The 3rd IF signal from the CODEC IC (IC9501) is detected at the AGC detector section in the DSP IC (IC9301). The output signal from the DSP IC is level-shifted at the level converter (IC9101) and applied to the D/A converter (IC9102). The AGC voltage is amplified at the buffer amplifi- er section in the IC9102 and applied to the MAIN unit to con- trol the AGC1 line.

When receiving strong signals, the detected voltage increas- es and the AGC1 voltage decreases. As the AGC1 voltage is used for the bias voltage of the IF amplifiers (MAIN unit; Q203, Q401, Q501), IF amplifier gain is decreased.

4-1-7 AF AMPLIFIER CIRCUIT (DSP AND MAIN UNITS)

The AF amplifier amplifies the audio signals to the suitable driving level for the speaker.

The AF signals from the DSP unit are applied to the AF amplifier (MAIN unit; IC1651, pin 3) via the “DSPO2” line. The signals are amplified at the other AF amplifier (IC1651, pin 5) after being passed through the low-pass filter. The sig- nals are applied to the AF mute switch (IC1602, pin 2), and then amplified at the AF power amplifier (IC1601, pin 1). The amplified signals are applied to the speaker (SP-26) after being passed through the speaker jack (J1451) via the “AFO” signal.

3rd IF signal

DSPI1

(12 kHz)

MAIN UNIT

IC9651b/a

Differential

converter

DSP UNIT

		IC9301
		DSP IC
CODEC IC (IC9501)
A/D	Level	D/A	Level
converter	converter	converter	converter

IC9701a

Active

filter

DSPO1

AF signals

• AGC CIRCUIT			From the
			antenna
DSPI1 IC1002 IF	Q501 IF	Q401 IF	Q203 IF
amp.	amp.	amp.	amp.
	IC1101

DSP

UNIT

AGC1	2	AGC	1
AGC2	6	AGC	7

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