Datasheet AD826 (Analog Devices) - 12

AD826 SINGLE-ENDED TO DIFFERENTIAL LINE DRIVER
Outstanding CMRR (> 80 dB @ 5 MHz), high bandwidth, wide
2V 200ns
supply voltage range, and the ability to drive heavy loads, make
100
the AD826 an ideal choice for many line driving applications.
90
In this application, the AD830 high speed video difference amp serves as the differential line receiver on the end of a back terminated, 50 ft., twisted-pair transmission line (see Figure 40). The overall system is configured in a gain of +1 and has a –3 dB bandwidth of 14 MHz. Figure 39 is the pulse response with a 2 V p-p, 1 MHz signal input.
10 0% 2V
Figure 39. Pulse Response
15V 0.01 F 15V 0.01 F 50 FEET TWISTED PAIR I Z = 72 0.1 F N 0.1 F 2.2 F 1/2 36 AD826 1.05k 36 VOUT BNC 5pF 1.05k AD830 1.05k 1.05k 36 36 5pF 1/2 AD826 0.01 F 0.01 F –15V 0.1 F –15V 0.1 F 2.2 F
Figure 40. Differential Line Driver
LOW DISTORTION LINE DRIVER 1.1k
The AD826 can quickly be turned into a powerful, low distor-
V
tion line driver (see Figure 41). In this arrangement the AD826
S 1 F 1k
can comfortably drive a 75 Ω back-terminated cable, with a 5 MHz, 2 V p-p input; all of this while achieving the harmonic
0.1 F
distortion performance outlined in the following table.
1/2 AD826 Configuration 2nd Harmonic RC
1. No Load –78.5 dBm
7.5 1k
2. 150 Ω RL Only –63.8 dBm 3. 150 Ω R
1k
L 7.5 Ω RC –70.4 dBm
RL 1/2 75
In this application one half of the AD826 operates at a gain of
AD826 75
2.1 and supplies the current to the load, while the other pro-
1 F 75
vides the overall system gain of 2. This is important for two reasons: the first is to keep the bandwidth of both amplifiers the
0.1 F
same, and the second is to preserve the AD826’s ability to oper- ate from low supply voltages. RC varies with the load and must Figure 41. Low Distortion Amplifier be chosen to satisfy the following equation: RC = MRL where M is defined by [(M+ 1) GS = GD] and GD = Driver’s Gain, GS = System Gain. –12– REV. C