M4670

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 9

www.unisonic.com.tw

QW-R502-442.b

APPLICATION INFORMATION (Cont.)

PROPER SELECTION OF EXTERNAL COMPONENTS

The M4670’s gain is set by the external resistors Ri, shown in Fig. 2, the gain of the equation by (2) is given.

When the gain of 2V/V (6dB), the THD+N performance of the best.

AV = 2 * 150 kΩ/ Ri (V/V) (2)

We recommend an external resistor Ri of the error within 1%, and the resistance should be close to M4670

input pins to keep two symmetrical inputs, which will help improve the M4670 noise suppression due to the good

CMRR of the M4670. Noise coupled onto input traces which are physically close to each other will be common mode

and easily rejected by the M4670. Input capacitors may be needed for some applications or when the source is

single- ended (Fig. 4, 6). Input capacitors are needed to block any DC voltage at the source so that the DC voltage

seen between the input terminals of the M4670 is 0V. Input capacitors create a high-pass filter with the input

resistors, Ri. The -3dB point of the high-pass filter is found using Equation (3) below.

Of course, the input capacitors can also be used to remove the low audio frequencies. When using the M4670

single-ended source, power supply noise on the ground is a +IN input pin capacitance-coupled input signals are on

the ground (Fig. 6~8). Setting the high-pass filter point above the power supply noise over the frequency of 217Hz in

the GMS mobile phone.

DIFFERENTIAL CIRCUIT CONFIGURATIONS

The M4670 can be used in many different circuit configurations. The most typical is the DC-coupled,

differential input configuration shown in Fig. 3. Equation(2) above is used to determine the value of the Ri resistors

for a desired gain.