ZHCSEH6E December 2002 – August 2020 THS7530
PRODUCTION DATA
A typical application circuit is shown in Figure 9-6. Two noteworthy aspects of this circuit are the customer’s automatic gain control (AGC) circuit and the THS7530 input bias circuit.
The proper design of the AGC circuit is essential for the THS7530 device to operate properly in the customer’s application. The method of detecting the amplitude of the differential output of the THS7530 device and creating the gain-control voltage, VG+, from the detected amplitude and the reference amplitude, Vref, are application-specific and beyond the scope of this document. The bandwidth of the amplitude of the THS7530 amplitude control is 15 MHz, which allows for rapid corrections of amplitude errors but which also allows noise from DC to 15 MHz to create an amplitude error. The trade-off between rapid amplitude correction and amplitude modulation due to noise is an important design consideration.
The input bias currents of the differential inputs of the THS7530 device are typically 20 µA. When the differential inputs are AC-coupled, the bias currents must be supplied as shown in Figure 9-6. In this circuit, the DC bias voltage is mid-supply and the AC differential input impedance is 50 Ω. The 0.1-µF capacitor between the two 24.9-Ω resistors creates an AC ground for the driving circuit.