Low voltage, time adjustable voice recording/playback circuit ISD1810

1 Main features

ISD1810 is a new product in the ISD series of voice recording and playback chips. It uses analog direct storage technology, so it has high fidelity and good sound quality. It can be recorded and played repeatedly 10,000 times; information can be stored for 100 years; ISD1810 uses a single power supply of 3V. , its recording and playback gap circuit can automatically enter the power saving state, and the maintenance current is only 0.5μA.

At the same time, the ISD1810 circuit also has four major characteristics:

The first is that the power supply is low. The Neurotic recommends an operating voltage of +3V (single power supply), and it can still work normally when it is as low as +2.7V. Therefore, it has broad market potential in high-end toys, greeting cards and other low-power applications.

Secondly, the recording and playback time is adjustable (8 to 16 seconds). The oscillation resistor (Rosc) of the ISD1810 is placed outside the integrated circuit chip. Therefore, the user can easily change the sampling frequency by simply changing the value of the oscillation resistor, thus adjusting the The length of the recording and playback time, that is to say, the larger the oscillation resistance, the lower the sampling frequency, the longer the recording and playback time, and of course the narrower the frequency band. If you want to pursue sound quality, you can choose a smaller oscillation resistance; if the recording and playback time is not enough, you can increase the oscillation resistance. This greatly enhances the practicality of the ISD circuit.

Third, the recording end and playback end of ISD1810 are both active at high level (positive pulse), which is significantly different from other series of ISD recording and playback chips. The recording and playback ends of the previous ISD 1100 and ISD1400 series were active at low level (negative pulse). It should be noted that except for the above differences between ISD 810 and ISD1100/ISD1400, other peripheral circuits such as microphones (MICs) are roughly the same. This may cause misconceptions among first-time users and lead to the phenomenon that normal recording and playback cannot occur when using this circuit.

Fourth, ISD1810 cannot be segmented. It does not have an address end, which reduces the trouble of dealing with the address end for users who do not need segmentation. But on the other hand, it may bring regrets to another part of users who need segmentation. In short, these characteristics of the ISD1810 circuit greatly expand the application scope of ISD, therefore, it is also widely welcomed by users.

2 ISD1810 pin arrangement and functional description

Figure 1 shows the pin arrangement diagram of ISD1810. The description of each pin is as follows:

VCCA, VCCD (+ power supply positive terminal): Within the chip, analog and digital circuits use different power buses and are led to the outer package respectively to reduce noise.

VSSA, VSSD: Ground terminal, the ground wires of digital and analog signals are also separated.

REC: recording end, high level is effective. Only when a high level appears on this end, regardless of whether the circuit is in playback or waiting state, the circuit will start recording immediately. And an EOM flag is given at the end to indicate that the replay operation stops here.

PLAYE: Edge-triggered playback terminal. When a rising edge occurs on this terminal, the chip starts to playback until the EOM end mark appears or the memory ends. Once playback starts, this end loses control function until playback ends.

PLAYL: Level triggers the playback terminal. On the rising edge of this terminal, the chip starts to playback. Once the high level cannot be maintained, the playback ends.

RECLED: Recording indication output terminal. When the chip is recording, this terminal turns to low level to drive the LED to light up.

MIC: Microphone input. This terminal is connected to the internal preamplifier of the circuit. The external microphone is coupled to this terminal through a capacitor. This capacitor and the circuit input impedance determine the frequency band low-frequency cutoff point of the chip.

MIC REF: The microphone parameter terminal is the automatic inverting input terminal of the preamplifier. The purpose of using the differential input form is to reduce noise and improve the common mode rejection ratio.

AGC: Automatic gain control terminal, used to compensate for changes in microphone input level amplitude to reduce distortion. Its response time is determined by the output impedance and bypass capacitor (4.7μF) of this terminal. A 4.7μF capacitor is also sufficient for release time.

SP+, SP-: speaker output terminals, which can directly drive 8Ω speakers. When used in single-ended mode, a coupling capacitor must be added between the output end and the speaker. The output power of single-ended mode is 1/4 of that of double-ended mode. During recording, both SP+ and SP- are in a high-impedance state.

XCLK: External clock input terminal. When in use, this terminal should be connected to a pull-down resistor. When not in use, it should be connected to ground.

ROSC: oscillation resistor access terminal, used to determine the length of recording and playback time, the recommended value is 100kΩ (10 seconds).

FT: Feed path. This mode allows external signals to drive the speakers. At this time, both the recording and playback terminals should be kept at a low level (Vss). Moreover, FT should be at a low level when not in use. Obviously there is a pull-down resistor inside this terminal, but when not in use, it still needs to be grounded again.

The operating temperature range of this circuit is 0~+50℃, and the recommended power supply voltage range is between 2.7~4.5V. Figure 2 shows a typical application circuit of ISD1810. Figure 3 shows the relationship between the oscillation resistance and recording time of the ISD1810.