Applied to various systems of ultrasonic imaging analog front-end design (1)

Ultrasonic imaging is a widely used method for medical imaging.

Traditional ultrasound imaging system uses the frequency of 2 ~ 15MHz, precision level to mm, and has been widely used in the diagnosis of fetal monitoring, and visceral disease, etc. Over the past 20 years, traditional tabletop ultrasonic system leads the medical ultrasound applications, this is because the ultrasonic system channel huge and signal handling a large quantity. Aging population, rising health care costs and the needs of emerging economies, led to innovative medical solutions to the growing demand.

Small size, low power and high-performance ultrasonic analog front end (AFE) and DSP is ultrasonic products manufacturers need.

More importantly, ultrasonic products manufacturers want a common to all kinds of system design, which allows the shortest of their development cycle and time to market, process.

Ultrasonic system structure

Ultrasonic system due to its functionality and performance.

For example, some high-end systems typically have 3D, 4D and harmonic imaging mode, while some low-end systems may only 2D B mode imaging and Doppler imaging mode. The main functional difference depends on the number of back-end. High-end ultrasonic system requires more, faster high-end DSP computational resources calls, thereby achieving near real-time signal processing. Obviously, in the high-end and portable systems share the signal processing unit. However, ignore the different performance requirements, ultrasonic systems generally have a similar reception channel.

As shown in Figure 1, ultrasonic systems receive analog front end by common modules, such as: low noise amplifier (LNA), time gain control (TGA) amplifier, voltage-controlled amplifier (VCA), programmable gain amplifier (PGA), low-pass filter as well as analog-digital converter (ADC).

In any case, the AFE's performance will greatly affect the performance of the entire system. Therefore, as long as the PIN to pin compatible packaging exists to meet the different performance requirements of AFE product, AFE design can be standardized, and various system be reused. This standardization in low-end system easily, such systems without special analog signal conditioning.

Figure 1 ultrasonic system chart

However, most of the AFE products meet ultrasonic product manufacturers of such requirements.

Therefore, you must select a separate chip to meet the CCM, and the various desktop system performance requirements. For example, desktop systems may allow a higher power, but had to lower noise and vice versa, so must be redesigned.

Some such as TI AFE5805 AFE devices maintain a novel of the same PIN.

The target application is portable and desktop of ultrasonic systems. PIN to pin compatible to allow ultrasonic products manufacturers to significantly save costs and speed to market of standardized design and AFE design innovative products.

Analog front end features and system performance relationship

Should always keep in mind designing ultrasonic system is a complex matter, and the characteristics of each of the AFE will affect the performance of the entire system.

For each system type balance select various parameters of capacity no doubt is an art.

Portable ultrasound system, power consumption is a key factor.

Low power consumption means lower battery provides a longer run time. However, it will affect other parameters, for example, the input signal range, enter the equivalent noise, harmonic distortion, although the performance is usually for portable (low-end) system is acceptable.

In addition to the power consumption, noise is ultrasonic AFE system designers need to consider the second factor.

Ultrasonic transducer for received signal level may 10 μ P V P ~ changes between 1VPP. To be able to detect the signal, the system, the higher the sensitivity. Input equivalent current and input equivalent voltage noise affects the system sensitivity. In General, 0.7 ~ 1.5nV/rt (Hz) (RTI) noise parameters are used to from high-end to low-end systems.

Some specific system application confirmed these noise parameters is sufficient to produce high-quality images.

Although you can use a more low-noise amplifier, but its ultimate ultrasonic image quality does not improve significantly because of the need to consider the input equivalent current noise and transmit/receive (T/R) switching noise. In addition to the input equivalent voltage noise, flicker noise (i.e. 1/f noise) imaging applications. In the mixing of continuous wave (CW) mode, low frequency noise spectrum moves to the carrier frequency, which reduces the relative frequency of the signal to noise ratio (SNR). With white noise performance of the amplifier is superior to its broad operating frequency.