In this project, we will design and build a Digital Signal Processor (DSP) system using the KM4164A-20 Dynamic RAM (DRAM) chip. While DRAMs are typically used for memory storage, they can also serve a vital role in DSP systems as high-speed, temporary memory buffers for fast data processing. This project will demonstrate how the KM4164A-20 can be integrated into a DSP circuit to process real-time signals such as audio or sensor data.

The KM4164A-20 is a 64K x 4-bit DRAM chip, meaning it stores 64,000 bits of data in a 4-bit wide configuration. While the chip may not have the same capabilities as a modern SRAM chip or Flash memory, its speed and the fact that it’s relatively easy to interface with makes it a good candidate for building basic DSP applications.

The goal of this project is to build a simple audio signal processing system using the KM4164A-20 as temporary data storage. This system will take in an analog audio signal, convert it to digital form, process it, and then output a modified version of the signal. The system could be used for effects such as amplification, tone control, or filtering.

Materials and Components:

1. KM4164A-20 DRAM Chip – Used for storing data temporarily during signal processing.

2. Analog-to-Digital Converter (ADC) – Converts the input analog signal to a digital signal that can be processed.

3. Digital-to-Analog Converter (DAC) – Converts the processed digital signal back into an analog signal for output.

4. Microcontroller or DSP Chip – Acts as the control unit to manage the data flow between the ADC, DRAM, and DAC.

5. Resistors and Capacitors – For signal conditioning and timing.

6. Op-Amps – Used to buffer and amplify analog signals.

7. Clock Oscillator – Provides the necessary timing for the DRAM and processing unit.

8. Power Supply – A regulated 5V or 12V supply to power the components.

9. Speaker – For audio output.

10. PCB or Breadboard – To mount and organize components.

11. Connectors and Wires – For interfacing components.

Project Overview:

The goal of this project is to use the KM4164A-20 DRAM chip in a digital signal processing (DSP) system, specifically for audio signal processing. The system will receive an audio input, convert it to a digital signal, store it in the DRAM, process the signal, and then output the processed signal as an analog signal to a speaker.

Here are the key steps involved:

1. Input Stage: The analog audio signal will be fed into the system through an analog-to-digital converter (ADC).

2. Data Storage: The KM4164A-20 will store the digital representation of the audio signal temporarily.

3. Signal Processing: A microcontroller or digital signal processor (DSP) chip will handle the processing of the data stored in the DRAM. This could involve tasks such as applying filters, adjusting amplitude, or adding effects.

4. Output Stage: The processed data will be sent to a digital-to-analog converter (DAC), which will convert the processed digital signal back to analog so it can be played through a speaker.

The entire system will function as a simple DSP processor for audio signals, demonstrating how DRAM can be used as part of a real-time signal processing chain.

Step 1: Understanding the KM4164A-20 DRAM

The KM4164A-20 is a 4-bit wide x 64K-word dynamic RAM chip, which means it can store 64K words of 4 bits each. In the context of this DSP project, the KM4164A-20 will act as a temporary data buffer that stores the audio signal as it’s being processed.

Key features of the KM4164A-20 include:

● 4-bit data width: This means the DRAM can store and retrieve data in 4-bit chunks. For audio processing, this means it can hold low-resolution samples of the audio signal at any given time.

● 64K memory: This allows the system to store a large number of audio samples for processing. This size is suitable for low to moderate-length audio processing tasks, such as simple effects or filtering.

● Refresh cycle: As a DRAM, the KM4164A-20 requires periodic refresh cycles to maintain the stored data. This means that our DSP system must be designed to ensure that the refresh process happens without interrupting the real-time signal processing.

In this project, we’ll interface the KM4164A-20 with a microcontroller to handle the refresh cycles and data read/write operations, as well as a clock generator to provide the necessary timing.

Step 2: Setting Up the Input Stage

The input stage of the DSP system will consist of an analog-to-digital converter (ADC) that converts the incoming audio signal to a digital format that can be processed by the DRAM.

● Op-Amp Buffer: The audio signal will first be buffered by an op-amp to ensure that the input signal has a high enough voltage and impedance for the ADC to sample correctly. The op-amp will also provide any necessary amplification if the audio signal is too weak.

● ADC: An ADC will be used to convert the analog audio signal into a digital form. A 12-bit ADC or better is typically used for audio processing, as this provides sufficient resolution to maintain high-quality audio. The digital output from the ADC will be fed into the KM4164A-20 DRAM chip.

● Clocking the ADC: The ADC will be clocked by the same clock source used for the KM4164A-20 to ensure synchronization between the sampling of the audio signal and the data storage in the DRAM.

Step 3: Interfacing with the KM4164A-20 DRAM

The KM4164A-20 will serve as the temporary data storage for the audio signal. The microcontroller or DSP chip will handle the read and write operations to the DRAM.

● Address Bus: The KM4164A-20 uses an address bus to select memory locations. The microcontroller or DSP will control this bus, ensuring that the audio data is written into memory in an organized manner.

● Data Bus: The KM4164A-20 has a 4-bit data width. This means that for each read or write operation, 4 bits of data will be transferred to or from the memory. For audio, we will store low-resolution samples of the signal, which can be used for basic processing such as volume control, basic filtering, or effects.

● Refresh Logic: As a dynamic RAM, the KM4164A-20 needs to be periodically refreshed to prevent data loss. A refresh timer or circuit will be used to handle this automatically. The refresh cycles need to be integrated with the overall DSP operation to ensure that the data is not overwritten during processing.

● Microcontroller or DSP Interface: A microcontroller or DSP chip will control the read and write operations to the DRAM. It will also manage the timing for refreshing the DRAM and synchronizing the input/output operations with the ADC and DAC.

Step 4: Signal Processing

Once the audio data is stored in the KM4164A-20, the microcontroller or DSP chip can process the data.

● Signal Manipulation: Simple operations like volume control, tone control, or low-pass filtering can be done by reading and writing the data in the DRAM. For example, adjusting the volume could involve multiplying the audio samples by a constant factor to reduce the amplitude, while applying a filter could involve reading a window of data and performing mathematical operations on it.

● Processing Loop: The microcontroller or DSP will continuously read from the KM4164A-20 and process the data in real-time. This could be done by using a FIFO (First In, First Out) buffer or similar memory management techniques to ensure that new samples are processed while old ones are output.

● Output: After processing the audio signal, the data is sent to the digital-to-analog converter (DAC) for conversion back into an analog signal.

Step 5: Output Stage

The output stage of the DSP system will consist of a digital-to-analog converter (DAC) that converts the processed digital signal back into an analog form that can drive a speaker.

● DAC: A 12-bit DAC or higher resolution is recommended for high-quality audio output. The digital signal is fed to the DAC, where it is converted into a voltage that can drive the speaker.

● Op-Amp Amplifier: Depending on the output level, an op-amp may be needed to amplify the signal to a level that is suitable for the speaker.

● Speaker: The final output will be sent to a speaker to produce audible sound.

Step 6: Testing and Tuning

After assembling the circuit, the next step is to test the system:

1. Powering Up: Power the system and check the connections.

2. Input Signal: Input a test audio signal (such as a sine wave or music) and check if it is properly converted into a digital form and stored in the KM4164A-20.

3. Signal Processing: Monitor the output signal to ensure that the processing operations (like volume control or filtering) are working correctly.

4. Output Signal: Ensure that the processed signal is properly converted back to analog and output through the speaker.

Conclusion

In this project, we have used the KM4164A-20 DRAM chip as a temporary data buffer in a simple digital signal processing system. By combining the KM4164A-20 with other components such as an ADC, DAC, microcontroller, and op-amps, we created a basic DSP system that can process audio signals in real-time.

This project demonstrates how DRAM can be used in real-time processing systems and how KM4164A-20 can be effectively integrated into DSP applications. By expanding this basic system, you could add more complex processing algorithms, more channels for multi-track audio processing, or even real-time effects like reverb and echo. The potential for future expansion is vast, and this project serves as a foundation for more advanced audio signal processing systems.