OPA835 datasheet(33/57 Pages) TI

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SIG-

IN-

SIG-

SIG+

IN+

OUT-

OUT+

SIG+

OPA2835

G = 1 +

´ ç

= V

1 +

+ V

OUT

OPA835, OPA2835

www.ti.com

SLOS713H – JANUARY 2011 – REVISED NOVEMBER 2015

Application Information (continued)

9.1.7 Differential to Differential Amplifier

Figure 68 shows a differential amplifier that is used to amplify differential signals. This circuit has high input

impedance and is often used in differential line driver applications where the signal source is a high impedance

driver (for example, a differential DAC) that must drive a line.

If we set VIN± = VCM + VSIG± then the output of the amplifier may be calculated according to Equation 6.

(6)

The signal gain of the circuit is set by:

, and VCM passes with unity gain. The amplifier in essence

combines two noninverting amplifiers into one differential amplifier with the RG resistor shared, which makes RG

effectively ½ its value when calculating the gain. The output signals are in-phase with the input signals.

Figure 68. Differential to Differential Amplifier

9.1.8 Gain Setting With OPA835 RUN Integrated Resistors

The OPA835 RUN package option includes integrated gain setting resistors for smallest possible footprint on a

printed circuit board (

≈ 2mm x 2mm). By adding circuit traces on the PCB, gains of +1, –1, –1.33, +2, +2.33, -3,

+4, –4, +5, –5.33, +6.33, –7, +8 and inverting attenuations of –0.1429, –0.1875, –0.25, –0.33, –0.75 can be

achieved.

Figure 69 shows a simplified view of how the OPA835IRUN integrated gain setting network is implemented.

Table 3 shows the required pin connections for various noninverting and inverting gains (reference Figure 53 and

Figure 54). Table 4 shows the required pin connections for various attenuations using the inverting amplifier

architecture (reference Figure 54). Due to ESD protection devices being used on all pins, the absolute maximum

and minimum input voltage range, VS– – 0.7 V to VS+ + 0.7 V, applies to the gain setting resistors, and so

attenuation of large input voltages will require external resistors to implement.

The gain setting resistors are laser trimmed to 1% tolerance with nominal values of 2.4 k

Ω, 1.8 kΩ, and 600 Ω.

They have excellent temperature coefficient and gain tracking is superior to using external gain setting resistors.

The 800

Ω and 1.25-pF capacitor in parallel with the 2.4-kΩ gain setting resistor provide compensation for best

stability and pulse response.

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