Based on ultrasonic attenuation compensation AD604 of typical application circuit (1)

Summary:

AD604 is AD company produced a low noise, high precision, two-channel, variable gain amplifier.

It has a gain of DB and gain control voltage proportional to the characteristics, ideal for ultrasonic instrument time gain compensation circuit applications. The article describes the characteristics of the AD604, structure and use methods, and introduces an approach based on the chip of ultrasonic attenuation compensation of the typical application circuit.

AD604 is Analog Devices (AD company) product.

And similar products, compared with the ultra low noise AD604, high precision, adjustable gain, and the gain in DB (dB) and gain control voltage proportional to the characteristic. And medical ultrasound instrument time gain control (TGC) circuit requires their gain and control voltage exponential relationships, gain of decibels (dB) and control voltage into a linear relationship. Therefore, in this regard, the AD604 is an ideal ultrasound TGC amplifier, it can effectively reduce the fed A/D converter dynamic range of the signal. AD604 's main characteristics are as follows:

¡Ñ low input noise, the maximum gain, the voltage and current noise respectively.

● 40MHz bandwidth (-3dB);

● Has two independent gain channel and gain of decibels (dB) and gain control of the proportional voltage;

● The gain for each channel can be programmed.

The preamplifier 14 dB gain available when 0 ~ + 48dB between adjustments; in pre-amplifier 20dB, gain in + 6 ~ + 54dB adjustable between;

● With 300 k Ω input resistance;

● Variable gain range is 20 ~ 40dB/V;

• Temperature and supply voltage changes, its gain very stable;

● You can single polarity gain control;

● When gain exceeds the maximum limit, the low power will automatically power off;

● Capable of directly driving A/D converter.

1 pin function

AD604 adopted 24 foot packaging and DIP, SOIC SSOP and three package, the pins are arranged as shown in Figure 1.

The PIN function as follows:

PAI1/PAI2: preamplifier is entered;

PAO1/PAO2: preamplifier output;

FBK1/FBK2: preamplifier feedback-end;

COM1/COM2: signal ground; when it received positive power preamplifier channels are closed;

-DSX1/-DSX2: differential signal input attenuator; negative side

+ DSX1/+ DSX2: differential signal input attenuator; positive side

VGN1/VGN2: gain control of inputs and power off-side.

Grounding, the attenuation of the channel is closed; otherwise, as the positive voltage increases, gain will gradually increase;

VREF: two-channel gain control.

When the voltage of + 2.5V, gain 20dB/V, and when the voltage of + 1.67V, gain 30dB/V;

VOCM: output signals of the common mode signal control client.

To determine which part of the circuit DC signal voltage value;

OUT1/OUT2: signal outputs;

VPOS/VNEG: received positive/negative power supply;

GND1 GND2 ground end/:.

2 internal structure and working principle

AD604 is a dual-channel variable gain amplifier.

It's every channel is represented by a low-noise preamplifier and a variable gain amplifier (XAMP). At the same time a XAMP consists of high-precision controlled differential attenuator, a gain control unit, a fixed-gain amplifier and a discrete components R3, R4, composed of VOCM common-mode voltage control units. Its principle is shown in Figure 2. AD604 of each channel provides a range of variable gain 48dB.