The SL6140 (Figure 3) is a high gain amplifier with an AGC control capable of reducing the gain of the amplifier by over 70dB. The gain is adjustable by applying a voltage to the AGC input via an external resistor (RAGC), the value of which adjusts the curve of gain reduction versus control voltage (see Figure 4). As the output stage of the amplifier is an open collector the maximum voltage gain is determined by RL. With load resistance of 1k the single ended voltage gain is 45dB and with a load resistance of 50 the voltage gain is 15dB (20log10 VOUT/VIN ). Another parameter that depends on the load resistance is the bandwidth: 25MHz for RL = 1k , as compared with 400MHz for RL = 50 . RL is chosen to give either the required bandwidth or voltage gain for the circuit.