MIC6211 Micrel, Inc. Applications InformationHigh-Pass FilterCommon-Mode Range and Output Voltage Figure 4 is an active filter with 20dB (10×) gain and a low- The input common-mode range of the MIC6211 is from the frequency cutoff of 10Hz. The high gain-bandwidth of the negative supply voltage to 1.2V below the positive supply MIC6211 allows operation beyond 100kHz. This filter con- voltage. The output voltage swings within 1V of the positive figuration is designed for split supplies. 0.1µF and negative supply voltage. Voltage Buffer 332k Figure 1 shows a standard voltage follower/buffer. The output voltage equals the input voltage. This circuit is used to buffer 1µF 1µF 4 V a high impedance signal source. This circuit works equally IN 1 V well with single or split supplies. 7.5k OUT 3 3 VIN 1 VOUT Figure 4a. High-Pass Filter 4 30 20 V 10 (dB) OUT= VIN 0 V OUT-10 Figure 1. Voltage Buffer -20 1 10 1 10 100 1k 100k Inverting Amplifier 1,000 10,000 100,000 FREQUENCY (Hz) Figure 2 shows an inverting amplifier with its gain set by the Figure 4b. High-Pass Filter Response ratio of two resistors. This circuit works best with split supplies, but will perform with single supply systems if the non-invert- Summing Amplifier ing input (+ input) is biased up above ground. Figure 5 is a single supply summing amplifier. In this con- R1 figuration, the output voltage is the sum of V1 and V2, minus R2 the sum of V3 and V4. By adding more resistors to either 4 VIN the inverting or non-inverting input, more voltages may be 1 VOUT summed. This single supply version has one important re- 3 striction: the sum of V1 and V2 must exceed the sum of V3 R1 V and V4, since the output voltage cannot pull below zero with OUT = –VIN R2 only a single supply. R Figure 2. Inverting Amplifer V1 R V2 3 Voltage Controlled Current Sink 1 VOUT R Figure 3 is a voltage controlled current sink. A buffer transis- 4 tor forces current through a programming resistor until the R R feedback loop is satisfied. Current flow is V V3 IN/R. This circuit R works with single or split supplies. V4 Al resistors are equal. 3 V VOUT = V1 + V2 – V3 – V4 IN 1 V1 + V2 > V3 + V4 for single supply operation 4 Figure 5. Summing Amplifier VIN R I R Figure 3. Voltage Controlled Current Sink MIC6211 6 April 2006